Test performance of optimization to unpack_trees() #18
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We're going to optimize unpack_trees() a bit in the following
patches. Let's add some tracing to measure how long it takes before
and after. This is the baseline ("git checkout -" on gcc.git, 80k
files on worktree)
0.018239226 s: read cache .git/index
0.052541655 s: preload index
0.001537598 s: refresh index
0.168167768 s: unpack trees
0.002897186 s: update worktree after a merge
0.131661745 s: repair cache-tree
0.075389117 s: write index, changed mask = 2a
0.111702023 s: unpack trees
0.000023245 s: update worktree after a merge
0.111793866 s: diff-index
0.587933288 s: git command: /home/pclouds/w/git/git checkout -
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In order to merge one or many trees with the index, unpack-trees code
walks multiple trees in parallel with the index and performs n-way
merge. If we find out at start of a directory that all trees are the
same (by comparing OID) and cache-tree happens to be available for
that directory as well, we could avoid walking the trees because we
already know what these trees contain: it's flattened in what's called
"the index".
The upside is of course a lot less I/O since we can potentially skip
lots of trees (think subtrees). We also save CPU because we don't have
to inflate and the apply deltas. The downside is of course more
fragile code since the logic in some functions are now duplicated
elsewhere.
"checkout -" with this patch on gcc.git:
baseline new
--------------------------------------------------------------------
0.018239226 0.019365414 s: read cache .git/index
0.052541655 0.049605548 s: preload index
0.001537598 0.001571695 s: refresh index
0.168167768 0.049677212 s: unpack trees
0.002897186 0.002845256 s: update worktree after a merge
0.131661745 0.136597522 s: repair cache-tree
0.075389117 0.075422517 s: write index, changed mask = 2a
0.111702023 0.032813253 s: unpack trees
0.000023245 0.000022002 s: update worktree after a merge
0.111793866 0.032933140 s: diff-index
0.587933288 0.398924370 s: git command: /home/pclouds/w/git/git
Another measurement from Ben's running "git checkout" with over 500k
trees (on the whole series):
baseline new
----------------------------------------------------------------------
0.535510167 0.556558733 s: read cache .git/index
0.3057373 0.3147105 s: initialize name hash
0.0184082 0.023558433 s: preload index
0.086910967 0.089085967 s: refresh index
7.889590767 2.191554433 s: unpack trees
0.120760833 0.131941267 s: update worktree after a merge
2.2583504 2.572663167 s: repair cache-tree
0.8916137 0.959495233 s: write index, changed mask = 28
3.405199233 0.2710663 s: unpack trees
0.000999667 0.0021554 s: update worktree after a merge
3.4063306 0.273318333 s: diff-index
16.9524923 9.462943133 s: git command: git.exe checkout
This command calls unpack_trees() twice, the first time on 2way merge
and the second 1way merge. In both times, "unpack trees" time is
reduced to one third. Overall time reduction is not that impressive of
course because index operations take a big chunk. And there's that
repair cache-tree line.
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
This is a micro optimization that probably only shines on repos with deep directory structure. Instead of allocating and freeing a new cache_entry in every iteration, we reuse the last one and only update the parts that are new each iteration. Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
With the new cache-tree, we could mostly avoid I/O (due to odb access) the code mostly becomes a loop of "check this, check that, add the entry to the index". We could skip a couple checks in this giant loop to go faster: - We know here that we're copying entries from the source index to the result one. All paths in the source index must have been validated at load time already (and we're not taking strange paths from tree objects) which means we can skip verify_path() without compromise. - We also know that D/F conflicts can't happen for all these entries (since cache-tree and all the trees are the same) so we can skip that as well. This gives rather nice speedups for "unpack trees" rows where "unpack trees" time is now cut in half compared to when traverse_by_cache_tree() is added, or 1/7 of the original "unpack trees" time. baseline cache-tree this patch -------------------------------------------------------------------- 0.018239226 0.019365414 0.020519621 s: read cache .git/index 0.052541655 0.049605548 0.048814384 s: preload index 0.001537598 0.001571695 0.001575382 s: refresh index 0.168167768 0.049677212 0.024719308 s: unpack trees 0.002897186 0.002845256 0.002805555 s: update worktree after a merge 0.131661745 0.136597522 0.134891617 s: repair cache-tree 0.075389117 0.075422517 0.074832291 s: write index, changed mask = 2a 0.111702023 0.032813253 0.008616479 s: unpack trees 0.000023245 0.000022002 0.000026630 s: update worktree after a merge 0.111793866 0.032933140 0.008714071 s: diff-index 0.587933288 0.398924370 0.380452871 s: git command: /home/pclouds/w/git/git Total saving of this new patch looks even less impressive, now that time spent in unpacking trees is so small. Which is why the next attempt should be on that "repair cache-tree" line. Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
ldennington
pushed a commit
to ldennington/git
that referenced
this pull request
Jun 2, 2021
The primary goal of this change is to stop leaking init_db_template_dir.
This leak can happen because:
1. git_init_db_config() allocates new memory into init_db_template_dir
without first freeing the existing value.
2. init_db_template_dir might already contain data, either because:
2.1 git_config() can be invoked twice with this callback in a single
process - at least 2 allocations are likely.
2.2 A single git_config() allocation can invoke the callback multiple
times for a given key (see further explanation in the function
docs) - each of those calls will trigger another leak.
The simplest fix for the leak would be to free(init_db_template_dir)
before overwriting it. Instead we choose to convert to fetching
init.templatedir via git_config_get_value() as that is more explicit,
more efficient, and avoids allocations (the returned result is owned by
the config cache, so we aren't responsible for freeing it).
If we remove init_db_template_dir, git_init_db_config() ends up being
responsible only for forwarding core.* config values to
platform_core_config(). However platform_core_config() already ignores
non-core.* config values, so we can safely remove git_init_db_config()
and invoke git_config() directly with platform_core_config() as the
callback.
The platform_core_config forwarding was originally added in:
2878533 (mingw: respect core.hidedotfiles = false in git-init again, 2019-03-11
And I suspect the potential for a leak existed since the original
implementation of git_init_db_config in:
90b4518 (Add `init.templatedir` configuration variable., 2010-02-17)
LSAN output from t0001:
Direct leak of 73 byte(s) in 1 object(s) allocated from:
#0 0x49a859 in realloc /home/abuild/rpmbuild/BUILD/llvm-11.0.0.src/build/../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:164:3
microsoft#1 0x9a7276 in xrealloc /home/ahunt/oss-fuzz/git/wrapper.c:126:8
microsoft#2 0x9362ad in strbuf_grow /home/ahunt/oss-fuzz/git/strbuf.c:98:2
microsoft#3 0x936eaa in strbuf_add /home/ahunt/oss-fuzz/git/strbuf.c:295:2
microsoft#4 0x868112 in strbuf_addstr /home/ahunt/oss-fuzz/git/./strbuf.h:304:2
microsoft#5 0x86a8ad in expand_user_path /home/ahunt/oss-fuzz/git/path.c:758:2
microsoft#6 0x720bb1 in git_config_pathname /home/ahunt/oss-fuzz/git/config.c:1287:10
microsoft#7 0x5960e2 in git_init_db_config /home/ahunt/oss-fuzz/git/builtin/init-db.c:161:11
microsoft#8 0x7255b8 in configset_iter /home/ahunt/oss-fuzz/git/config.c:1982:7
microsoft#9 0x7253fc in repo_config /home/ahunt/oss-fuzz/git/config.c:2311:2
microsoft#10 0x725ca7 in git_config /home/ahunt/oss-fuzz/git/config.c:2399:2
microsoft#11 0x593e8d in create_default_files /home/ahunt/oss-fuzz/git/builtin/init-db.c:225:2
microsoft#12 0x5935c6 in init_db /home/ahunt/oss-fuzz/git/builtin/init-db.c:449:11
microsoft#13 0x59588e in cmd_init_db /home/ahunt/oss-fuzz/git/builtin/init-db.c:714:9
microsoft#14 0x4cd60d in run_builtin /home/ahunt/oss-fuzz/git/git.c:453:11
microsoft#15 0x4cb2da in handle_builtin /home/ahunt/oss-fuzz/git/git.c:704:3
microsoft#16 0x4ccc37 in run_argv /home/ahunt/oss-fuzz/git/git.c:771:4
microsoft#17 0x4cac29 in cmd_main /home/ahunt/oss-fuzz/git/git.c:902:19
microsoft#18 0x69c4de in main /home/ahunt/oss-fuzz/git/common-main.c:52:11
microsoft#19 0x7f23552d6349 in __libc_start_main (/lib64/libc.so.6+0x24349)
Signed-off-by: Andrzej Hunt <ajrhunt@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
ldennington
pushed a commit
to ldennington/git
that referenced
this pull request
Jun 2, 2021
limit_list() iterates over the original revs->commits list, and consumes
many of its entries via pop_commit. However we might stop iterating over
the list early (e.g. if we realise that the rest of the list is
uninteresting). If we do stop iterating early, list will be pointing to
the unconsumed portion of revs->commits - and we need to free this list
to avoid a leak. (revs->commits itself will be an invalid pointer: it
will have been free'd during the first pop_commit.)
However the list pointer is later reused to iterate over our new list,
but only for the limiting_can_increase_treesame() branch. We therefore
need to introduce a new variable for that branch - and while we're here
we can rename the original list to original_list as that makes its
purpose more obvious.
This leak was found while running t0090. It's not likely to be very
impactful, but it can happen quite early during some checkout
invocations, and hence seems to be worth fixing:
Direct leak of 16 byte(s) in 1 object(s) allocated from:
#0 0x49a85d in malloc ../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
microsoft#1 0x9ac084 in do_xmalloc wrapper.c:41:8
microsoft#2 0x9ac05a in xmalloc wrapper.c:62:9
microsoft#3 0x7175d6 in commit_list_insert commit.c:540:33
microsoft#4 0x71800f in commit_list_insert_by_date commit.c:604:9
microsoft#5 0x8f8d2e in process_parents revision.c:1128:5
microsoft#6 0x8f2f2c in limit_list revision.c:1418:7
microsoft#7 0x8f210e in prepare_revision_walk revision.c:3577:7
microsoft#8 0x514170 in orphaned_commit_warning builtin/checkout.c:1185:6
microsoft#9 0x512f05 in switch_branches builtin/checkout.c:1250:3
microsoft#10 0x50f8de in checkout_branch builtin/checkout.c:1646:9
microsoft#11 0x50ba12 in checkout_main builtin/checkout.c:2003:9
microsoft#12 0x5086c0 in cmd_checkout builtin/checkout.c:2055:8
microsoft#13 0x4cd91d in run_builtin git.c:467:11
microsoft#14 0x4cb5f3 in handle_builtin git.c:719:3
microsoft#15 0x4ccf47 in run_argv git.c:808:4
microsoft#16 0x4caf49 in cmd_main git.c:939:19
microsoft#17 0x69dc0e in main common-main.c:52:11
microsoft#18 0x7faaabd0e349 in __libc_start_main (/lib64/libc.so.6+0x24349)
Indirect leak of 48 byte(s) in 3 object(s) allocated from:
#0 0x49a85d in malloc ../projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
microsoft#1 0x9ac084 in do_xmalloc wrapper.c:41:8
microsoft#2 0x9ac05a in xmalloc wrapper.c:62:9
microsoft#3 0x717de6 in commit_list_append commit.c:1609:35
microsoft#4 0x8f1f9b in prepare_revision_walk revision.c:3554:12
microsoft#5 0x514170 in orphaned_commit_warning builtin/checkout.c:1185:6
microsoft#6 0x512f05 in switch_branches builtin/checkout.c:1250:3
microsoft#7 0x50f8de in checkout_branch builtin/checkout.c:1646:9
microsoft#8 0x50ba12 in checkout_main builtin/checkout.c:2003:9
microsoft#9 0x5086c0 in cmd_checkout builtin/checkout.c:2055:8
microsoft#10 0x4cd91d in run_builtin git.c:467:11
microsoft#11 0x4cb5f3 in handle_builtin git.c:719:3
microsoft#12 0x4ccf47 in run_argv git.c:808:4
microsoft#13 0x4caf49 in cmd_main git.c:939:19
microsoft#14 0x69dc0e in main common-main.c:52:11
microsoft#15 0x7faaabd0e349 in __libc_start_main (/lib64/libc.so.6+0x24349)
Signed-off-by: Andrzej Hunt <ajrhunt@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
derrickstolee
pushed a commit
that referenced
this pull request
Oct 7, 2021
In a sparse index it is possible for the tree that is being verified
to be freed while it is being verified. This happens when the index is
sparse but the cache tree is not and index_name_pos() looks up a path
from the cache tree that is a descendant of a sparse index entry. That
triggers a call to ensure_full_index() which frees the cache tree that
is being verified. Carrying on trying to verify the tree after this
results in a use-after-free bug. Instead restart the verification if a
sparse index is converted to a full index. This bug is triggered by a
call to reset_head() in "git rebase --apply". Thanks to René Scharfe
and Derrick Stolee for their help analyzing the problem.
==74345==ERROR: AddressSanitizer: heap-use-after-free on address 0x606000001b20 at pc 0x557cbe82d3a2 bp 0x7ffdfee08090 sp 0x7ffdfee08080
READ of size 4 at 0x606000001b20 thread T0
#0 0x557cbe82d3a1 in verify_one /home/phil/src/git/cache-tree.c:863
#1 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#2 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#3 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#4 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
#5 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
#6 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
#7 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#8 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#9 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#10 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#11 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#12 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#13 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
#14 0x557cbe5bcb8d in _start (/home/phil/src/git/git+0x1b9b8d)
0x606000001b20 is located 0 bytes inside of 56-byte region [0x606000001b20,0x606000001b58)
freed by thread T0 here:
#0 0x7fdd4bacff19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
#1 0x557cbe82af60 in cache_tree_free /home/phil/src/git/cache-tree.c:35
#2 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#3 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#4 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#5 0x557cbeb2557a in ensure_full_index /home/phil/src/git/sparse-index.c:310
#6 0x557cbea45c4a in index_name_stage_pos /home/phil/src/git/read-cache.c:588
#7 0x557cbe82ce37 in verify_one /home/phil/src/git/cache-tree.c:850
#8 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#9 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#10 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#11 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
#12 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
#13 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
#14 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#15 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#16 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#17 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#18 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#19 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#20 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
previously allocated by thread T0 here:
#0 0x7fdd4bad0459 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
#1 0x557cbebc1807 in xcalloc /home/phil/src/git/wrapper.c:140
#2 0x557cbe82b7d8 in cache_tree /home/phil/src/git/cache-tree.c:17
#3 0x557cbe82b7d8 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:763
#4 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
#5 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
#6 0x557cbe8304e1 in prime_cache_tree /home/phil/src/git/cache-tree.c:779
#7 0x557cbeab7fa7 in reset_head /home/phil/src/git/reset.c:85
#8 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#9 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#10 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#11 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#12 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#13 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#14 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
neerajsi-msft
pushed a commit
to neerajsi-msft/git
that referenced
this pull request
Oct 26, 2021
In a sparse index it is possible for the tree that is being verified
to be freed while it is being verified. This happens when the index is
sparse but the cache tree is not and index_name_pos() looks up a path
from the cache tree that is a descendant of a sparse index entry. That
triggers a call to ensure_full_index() which frees the cache tree that
is being verified. Carrying on trying to verify the tree after this
results in a use-after-free bug. Instead restart the verification if a
sparse index is converted to a full index. This bug is triggered by a
call to reset_head() in "git rebase --apply". Thanks to René Scharfe
and Derrick Stolee for their help analyzing the problem.
==74345==ERROR: AddressSanitizer: heap-use-after-free on address 0x606000001b20 at pc 0x557cbe82d3a2 bp 0x7ffdfee08090 sp 0x7ffdfee08080
READ of size 4 at 0x606000001b20 thread T0
#0 0x557cbe82d3a1 in verify_one /home/phil/src/git/cache-tree.c:863
#1 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#2 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#3 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#4 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
microsoft#5 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
microsoft#6 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
microsoft#7 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
microsoft#8 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
microsoft#9 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
microsoft#10 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
microsoft#11 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
microsoft#12 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
microsoft#13 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
microsoft#14 0x557cbe5bcb8d in _start (/home/phil/src/git/git+0x1b9b8d)
0x606000001b20 is located 0 bytes inside of 56-byte region [0x606000001b20,0x606000001b58)
freed by thread T0 here:
#0 0x7fdd4bacff19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
#1 0x557cbe82af60 in cache_tree_free /home/phil/src/git/cache-tree.c:35
microsoft#2 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
microsoft#3 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
microsoft#4 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
microsoft#5 0x557cbeb2557a in ensure_full_index /home/phil/src/git/sparse-index.c:310
microsoft#6 0x557cbea45c4a in index_name_stage_pos /home/phil/src/git/read-cache.c:588
microsoft#7 0x557cbe82ce37 in verify_one /home/phil/src/git/cache-tree.c:850
microsoft#8 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#9 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#10 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
microsoft#11 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
microsoft#12 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
microsoft#13 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
microsoft#14 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
microsoft#15 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
microsoft#16 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
microsoft#17 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
microsoft#18 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
microsoft#19 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
microsoft#20 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
previously allocated by thread T0 here:
#0 0x7fdd4bad0459 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
#1 0x557cbebc1807 in xcalloc /home/phil/src/git/wrapper.c:140
microsoft#2 0x557cbe82b7d8 in cache_tree /home/phil/src/git/cache-tree.c:17
microsoft#3 0x557cbe82b7d8 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:763
microsoft#4 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
microsoft#5 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
microsoft#6 0x557cbe8304e1 in prime_cache_tree /home/phil/src/git/cache-tree.c:779
microsoft#7 0x557cbeab7fa7 in reset_head /home/phil/src/git/reset.c:85
microsoft#8 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
microsoft#9 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
microsoft#10 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
microsoft#11 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
microsoft#12 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
microsoft#13 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
microsoft#14 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho
pushed a commit
that referenced
this pull request
Oct 30, 2021
In a sparse index it is possible for the tree that is being verified
to be freed while it is being verified. This happens when the index is
sparse but the cache tree is not and index_name_pos() looks up a path
from the cache tree that is a descendant of a sparse index entry. That
triggers a call to ensure_full_index() which frees the cache tree that
is being verified. Carrying on trying to verify the tree after this
results in a use-after-free bug. Instead restart the verification if a
sparse index is converted to a full index. This bug is triggered by a
call to reset_head() in "git rebase --apply". Thanks to René Scharfe
and Derrick Stolee for their help analyzing the problem.
==74345==ERROR: AddressSanitizer: heap-use-after-free on address 0x606000001b20 at pc 0x557cbe82d3a2 bp 0x7ffdfee08090 sp 0x7ffdfee08080
READ of size 4 at 0x606000001b20 thread T0
#0 0x557cbe82d3a1 in verify_one /home/phil/src/git/cache-tree.c:863
#1 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#2 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#3 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#4 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
#5 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
#6 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
#7 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#8 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#9 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#10 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#11 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#12 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#13 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
#14 0x557cbe5bcb8d in _start (/home/phil/src/git/git+0x1b9b8d)
0x606000001b20 is located 0 bytes inside of 56-byte region [0x606000001b20,0x606000001b58)
freed by thread T0 here:
#0 0x7fdd4bacff19 in __interceptor_free /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:127
#1 0x557cbe82af60 in cache_tree_free /home/phil/src/git/cache-tree.c:35
#2 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#3 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#4 0x557cbe82aee5 in cache_tree_free /home/phil/src/git/cache-tree.c:31
#5 0x557cbeb2557a in ensure_full_index /home/phil/src/git/sparse-index.c:310
#6 0x557cbea45c4a in index_name_stage_pos /home/phil/src/git/read-cache.c:588
#7 0x557cbe82ce37 in verify_one /home/phil/src/git/cache-tree.c:850
#8 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#9 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#10 0x557cbe82ca9d in verify_one /home/phil/src/git/cache-tree.c:840
#11 0x557cbe830a2b in cache_tree_verify /home/phil/src/git/cache-tree.c:910
#12 0x557cbea53741 in write_locked_index /home/phil/src/git/read-cache.c:3250
#13 0x557cbeab7fdd in reset_head /home/phil/src/git/reset.c:87
#14 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#15 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#16 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#17 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#18 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#19 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#20 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
previously allocated by thread T0 here:
#0 0x7fdd4bad0459 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
#1 0x557cbebc1807 in xcalloc /home/phil/src/git/wrapper.c:140
#2 0x557cbe82b7d8 in cache_tree /home/phil/src/git/cache-tree.c:17
#3 0x557cbe82b7d8 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:763
#4 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
#5 0x557cbe82b837 in prime_cache_tree_rec /home/phil/src/git/cache-tree.c:764
#6 0x557cbe8304e1 in prime_cache_tree /home/phil/src/git/cache-tree.c:779
#7 0x557cbeab7fa7 in reset_head /home/phil/src/git/reset.c:85
#8 0x557cbe72147f in cmd_rebase builtin/rebase.c:2074
#9 0x557cbe5bd151 in run_builtin /home/phil/src/git/git.c:461
#10 0x557cbe5bd151 in handle_builtin /home/phil/src/git/git.c:714
#11 0x557cbe5c0503 in run_argv /home/phil/src/git/git.c:781
#12 0x557cbe5c0503 in cmd_main /home/phil/src/git/git.c:912
#13 0x557cbe5bad28 in main /home/phil/src/git/common-main.c:52
#14 0x7fdd4b82eb24 in __libc_start_main (/usr/lib/libc.so.6+0x27b24)
Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
ldennington
pushed a commit
to ldennington/git
that referenced
this pull request
Jan 20, 2022
When fetching packfiles, we write a bunch of lockfiles for the packfiles
we're writing into the repository. In order to not leave behind any
cruft in case we exit or receive a signal, we register both an exit
handler as well as signal handlers for common signals like SIGINT. These
handlers will then unlink the locks and free the data structure tracking
them. We have observed a deadlock in this logic though:
(gdb) bt
#0 __lll_lock_wait_private () at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:95
microsoft#1 0x00007f4932bea2cd in _int_free (av=0x7f4932f2eb20 <main_arena>, p=0x3e3e4200, have_lock=0) at malloc.c:3969
microsoft#2 0x00007f4932bee58c in __GI___libc_free (mem=<optimized out>) at malloc.c:2975
microsoft#3 0x0000000000662ab1 in string_list_clear ()
microsoft#4 0x000000000044f5bc in unlock_pack_on_signal ()
microsoft#5 <signal handler called>
microsoft#6 _int_free (av=0x7f4932f2eb20 <main_arena>, p=<optimized out>, have_lock=0) at malloc.c:4024
microsoft#7 0x00007f4932bee58c in __GI___libc_free (mem=<optimized out>) at malloc.c:2975
microsoft#8 0x000000000065afd5 in strbuf_release ()
microsoft#9 0x000000000066ddb9 in delete_tempfile ()
microsoft#10 0x0000000000610d0b in files_transaction_cleanup.isra ()
microsoft#11 0x0000000000611718 in files_transaction_abort ()
microsoft#12 0x000000000060d2ef in ref_transaction_abort ()
microsoft#13 0x000000000060d441 in ref_transaction_prepare ()
microsoft#14 0x000000000060e0b5 in ref_transaction_commit ()
microsoft#15 0x00000000004511c2 in fetch_and_consume_refs ()
microsoft#16 0x000000000045279a in cmd_fetch ()
microsoft#17 0x0000000000407c48 in handle_builtin ()
microsoft#18 0x0000000000408df2 in cmd_main ()
microsoft#19 0x00000000004078b5 in main ()
The process was killed with a signal, which caused the signal handler to
kick in and try free the data structures after we have unlinked the
locks. It then deadlocks while calling free(3P).
The root cause of this is that it is not allowed to call certain
functions in async-signal handlers, as specified by signal-safety(7).
Next to most I/O functions, this list of disallowed functions also
includes memory-handling functions like malloc(3P) and free(3P) because
they may not be reentrant. As a result, if we execute such functions in
the signal handler, then they may operate on inconistent state and fail
in unexpected ways.
Fix this bug by not calling non-async-signal-safe functions when running
in the signal handler. We're about to re-raise the signal anyway and
will thus exit, so it's not much of a problem to keep the string list of
lockfiles untouched. Note that it's fine though to call unlink(2), so
we'll still clean up the lockfiles correctly.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Reviewed-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
dscho
added a commit
that referenced
this pull request
Oct 9, 2024
An internal customer reported a segfault when running `git sparse-checkout set` with the `index.sparse` config enabled. I was unable to reproduce it locally, but with their help we debugged into the failing process and discovered the following stacktrace: ``` #0 0x00007ff6318fb7b0 in rehash (map=0x3dfb00d0440, newsize=1048576) at hashmap.c:125 #1 0x00007ff6318fbc66 in hashmap_add (map=0x3dfb00d0440, entry=0x3dfb5c58bc8) at hashmap.c:247 #2 0x00007ff631937a70 in hash_index_entry (istate=0x3dfb00d0400, ce=0x3dfb5c58bc8) at name-hash.c:122 #3 0x00007ff631938a2f in add_name_hash (istate=0x3dfb00d0400, ce=0x3dfb5c58bc8) at name-hash.c:638 #4 0x00007ff631a064de in set_index_entry (istate=0x3dfb00d0400, nr=8291, ce=0x3dfb5c58bc8) at sparse-index.c:255 #5 0x00007ff631a06692 in add_path_to_index (oid=0x5ff130, base=0x5ff580, path=0x3dfb4b725da "<redacted>", mode=33188, context=0x5ff570) at sparse-index.c:307 #6 0x00007ff631a3b48c in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41f60, base=0x5ff580, depth=2, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:46 #7 0x00007ff631a3b60b in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41e80, base=0x5ff580, depth=1, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:80 #8 0x00007ff631a3b60b in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41ac8, base=0x5ff580, depth=0, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:80 #9 0x00007ff631a06a95 in expand_index (istate=0x3dfb00d0100, pl=0x0) at sparse-index.c:422 #10 0x00007ff631a06cbd in ensure_full_index (istate=0x3dfb00d0100) at sparse-index.c:456 #11 0x00007ff631990d08 in index_name_stage_pos (istate=0x3dfb00d0100, name=0x3dfb0020080 "algorithm/levenshtein", namelen=21, stage=0, search_mode=EXPAND_SPARSE) at read-cache.c:556 #12 0x00007ff631990d6c in index_name_pos (istate=0x3dfb00d0100, name=0x3dfb0020080 "algorithm/levenshtein", namelen=21) at read-cache.c:566 #13 0x00007ff63180dbb5 in sanitize_paths (argc=185, argv=0x3dfb0030018, prefix=0x0, skip_checks=0) at builtin/sparse-checkout.c:756 #14 0x00007ff63180de50 in sparse_checkout_set (argc=185, argv=0x3dfb0030018, prefix=0x0) at builtin/sparse-checkout.c:860 #15 0x00007ff63180e6c5 in cmd_sparse_checkout (argc=186, argv=0x3dfb0030018, prefix=0x0) at builtin/sparse-checkout.c:1063 #16 0x00007ff6317234cb in run_builtin (p=0x7ff631ad9b38 <commands+2808>, argc=187, argv=0x3dfb0030018) at git.c:548 #17 0x00007ff6317239c0 in handle_builtin (argc=187, argv=0x3dfb0030018) at git.c:808 #18 0x00007ff631723c7d in run_argv (argcp=0x5ffdd0, argv=0x5ffd78) at git.c:877 #19 0x00007ff6317241d1 in cmd_main (argc=187, argv=0x3dfb0030018) at git.c:1017 #20 0x00007ff631838b60 in main (argc=190, argv=0x3dfb0030000) at common-main.c:64 ``` The very bottom of the stack being the `rehash()` method from `hashmap.c` as called within the `name-hash` API made me look at where these hashmaps were being used in the sparse index logic. These were being copied across indexes, which seems dangerous. Indeed, clearing these hashmaps and setting them as not initialized fixes the segfault. The second commit is a response to a test failure that happens in `t1092-sparse-checkout-compatibility.sh` where `git stash pop` starts to fail because the underlying `git checkout-index` process fails due to colliding files. Passing the `-f` flag appears to work, but it's unclear why this name-hash change causes that change in behavior.
dscho
added a commit
that referenced
this pull request
Oct 9, 2024
An internal customer reported a segfault when running `git sparse-checkout set` with the `index.sparse` config enabled. I was unable to reproduce it locally, but with their help we debugged into the failing process and discovered the following stacktrace: ``` #0 0x00007ff6318fb7b0 in rehash (map=0x3dfb00d0440, newsize=1048576) at hashmap.c:125 #1 0x00007ff6318fbc66 in hashmap_add (map=0x3dfb00d0440, entry=0x3dfb5c58bc8) at hashmap.c:247 #2 0x00007ff631937a70 in hash_index_entry (istate=0x3dfb00d0400, ce=0x3dfb5c58bc8) at name-hash.c:122 #3 0x00007ff631938a2f in add_name_hash (istate=0x3dfb00d0400, ce=0x3dfb5c58bc8) at name-hash.c:638 #4 0x00007ff631a064de in set_index_entry (istate=0x3dfb00d0400, nr=8291, ce=0x3dfb5c58bc8) at sparse-index.c:255 #5 0x00007ff631a06692 in add_path_to_index (oid=0x5ff130, base=0x5ff580, path=0x3dfb4b725da "<redacted>", mode=33188, context=0x5ff570) at sparse-index.c:307 #6 0x00007ff631a3b48c in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41f60, base=0x5ff580, depth=2, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:46 #7 0x00007ff631a3b60b in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41e80, base=0x5ff580, depth=1, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:80 #8 0x00007ff631a3b60b in read_tree_at (r=0x7ff631c026a0 <the_repo>, tree=0x3dfb5b41ac8, base=0x5ff580, depth=0, pathspec=0x5ff5a0, fn=0x7ff631a064e5 <add_path_to_index>, context=0x5ff570) at tree.c:80 #9 0x00007ff631a06a95 in expand_index (istate=0x3dfb00d0100, pl=0x0) at sparse-index.c:422 #10 0x00007ff631a06cbd in ensure_full_index (istate=0x3dfb00d0100) at sparse-index.c:456 #11 0x00007ff631990d08 in index_name_stage_pos (istate=0x3dfb00d0100, name=0x3dfb0020080 "algorithm/levenshtein", namelen=21, stage=0, search_mode=EXPAND_SPARSE) at read-cache.c:556 #12 0x00007ff631990d6c in index_name_pos (istate=0x3dfb00d0100, name=0x3dfb0020080 "algorithm/levenshtein", namelen=21) at read-cache.c:566 #13 0x00007ff63180dbb5 in sanitize_paths (argc=185, argv=0x3dfb0030018, prefix=0x0, skip_checks=0) at builtin/sparse-checkout.c:756 #14 0x00007ff63180de50 in sparse_checkout_set (argc=185, argv=0x3dfb0030018, prefix=0x0) at builtin/sparse-checkout.c:860 #15 0x00007ff63180e6c5 in cmd_sparse_checkout (argc=186, argv=0x3dfb0030018, prefix=0x0) at builtin/sparse-checkout.c:1063 #16 0x00007ff6317234cb in run_builtin (p=0x7ff631ad9b38 <commands+2808>, argc=187, argv=0x3dfb0030018) at git.c:548 #17 0x00007ff6317239c0 in handle_builtin (argc=187, argv=0x3dfb0030018) at git.c:808 #18 0x00007ff631723c7d in run_argv (argcp=0x5ffdd0, argv=0x5ffd78) at git.c:877 #19 0x00007ff6317241d1 in cmd_main (argc=187, argv=0x3dfb0030018) at git.c:1017 #20 0x00007ff631838b60 in main (argc=190, argv=0x3dfb0030000) at common-main.c:64 ``` The very bottom of the stack being the `rehash()` method from `hashmap.c` as called within the `name-hash` API made me look at where these hashmaps were being used in the sparse index logic. These were being copied across indexes, which seems dangerous. Indeed, clearing these hashmaps and setting them as not initialized fixes the segfault. The second commit is a response to a test failure that happens in `t1092-sparse-checkout-compatibility.sh` where `git stash pop` starts to fail because the underlying `git checkout-index` process fails due to colliding files. Passing the `-f` flag appears to work, but it's unclear why this name-hash change causes that change in behavior.
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Do not merge. Just a PR to generate a build to be used to get a performance test on the optimization.