[2.1.12 backport] Fix buffered/direct/mmap I/O race #14750
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We should also include dd108f5, which fixes the static analyzer complaint about what should be a real bug that occurs after this is merged. |
Good call! I've picked that commit and pushed it here. Thanks! |
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Can you rebase this on the new zfs-2.1.12-staging. branch. |
When a page is faulted in for memory mapped I/O the page lock may be dropped before it has been read and marked up to date. If a buffered read encounters such a page in mappedread() it must wait until the page has been updated. Failure to do so will result in a panic on debug builds and incorrect data on production builds. The critical part of this change is in mappedread() where pages which are not up to date are now handled. Additionally, it includes the following simplifications. - zfs_getpage() and zfs_fillpage() could be passed an array of pages. This could be more efficient if it was used but in practice only a single page was ever provided. These interfaces were simplified to acknowledge that. - update_pages() was modified to correctly set the PG_error bit on a page when it cannot be read by dmu_read(). - Setting PG_error and PG_uptodate was moved to zfs_fillpage() from zpl_readpage_common(). This is consistent with the handling in update_pages() and mappedread(). - Minor additional refactoring to comments and variable declarations to improve readability. - Add a test case to exercise concurrent buffered, direct, and mmap IO to the same file. - Reduce the mmap_sync test case default run time. Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu> Reviewed-by: Brian Atkinson <batkinson@lanl.gov> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes openzfs#13608 Closes openzfs#14498
After 89cd219 was merged, Clang's static analyzer began complaining about a dead assignment in `zfs_fillpage()`. Upon inspection, I noticed that the dead assignment was because we are not using the calculated io_len that we should use to avoid asking the DMU to read past the end of a file. This should result in `dmu_buf_hold_array_by_dnode()` calling `zfs_panic_recover()`. This issue predates 89cd219, but its simplification of zfs_fillpage() eliminated the only use of the assignment to io_len, which made Clang's static analyzer complain about the issue. Also, as a precaution, we add an assertion that io_offset < i_size. If this ever fails, bad things will happen. Otherwise, we are blindly trusting the kernel not to give us invalid offsets. We continue to blindly trust it on non-debug kernels. Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Reviewed-by: Brian Atkinson <batkinson@lanl.gov> Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu> Closes openzfs#14534
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@behlendorf done, thanks. |
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Status: Accepted
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Description
Backporting #14498 and #14534 to 2.1.
How Has This Been Tested?
Compiles OK. Test suite will do the rest.
Types of changes
Checklist:
Signed-off-by.