Missing EINTR handling on macOS for opendir/readdir/closedir syscalls

[Therzok]

Description

It seems that under certain conditions, the opendir, readdir, closedir can set errno to EINTR.

These 3 syscalls are the only ones I can see not handling EINTR:

runtime/src/libraries/Native/Unix/System.Native/pal_io.c

Line 474 in e98fb61

DIR* SystemNative_OpenDir(const char* path)

Note: it is not documented in the man pages, but it seems to be a problem in practice.

Configuration

Mono 2020-02, macOS, x64. Not specific to this.

Regression?

Only started happening with macOS Big Sur.

Other information

See this gist for an exception being bubbled on mono which is using the same source as dotnet/runtime.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[danmoseley]

closedir does document EINTR at least here https://www.man7.org/linux/man-pages/man3/closedir.3p.html. Not sure about the others.

[Therzok]

opendir is the one being called in the exception stack trace linked above, so I think it's fair to consider it set.

[danmoseley]

@janvorli any thoghts here? I guess worst case, it is unnecessary code. My only thought (waves hands) that if EINTR is actually a bug here, then who knows if it would just continue to return EINTR, and we would hang.

[janvorli]

It seems that opendir can return EINTR on macOS as far as I can tell from https://opensource.apple.com/source/Libc/Libc-1439.40.11/gen/FreeBSD/opendir.c.auto.html. It internally calls fstatfs which can return EINTR according to its documentation.
As for closedir, it calls regular close on a handle, thus the behavior of close controls the error code. There is an interesting discussion on EINTR and close and it seems that it should be ignored. See https://sourceware.org/bugzilla/show_bug.cgi?id=14627.
Regarding the readdir, it is not clear to me whether it can return EINTR or not.

Overall, it seems to me it would be safe to handle it at opendir / readdir and eat it at closedir.

[danmoseley]

Thanks @janvorli . @Therzok would you like to offer a PR?

[Therzok]

@janvorli I dug a bit into the macos source code and the , and via: getdirentries64 -> getdirentriescommon -> vnode_getwithref -> vnode_getiocount -> msleep -> _sleep we got a possible EINTR.

I'll send a PR with the fixes.