Re: [Bug 205833] fsfreeze blocks close(fd) on xfs sometimes

[Brian Foster <bfoster@redhat.com>]

On Tue, Dec 17, 2019 at 09:34:34AM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=205833
> 
> --- Comment #2 from Stefan @dns2utf8 Schindler (kernel.org@estada.ch) ---
> Hi Brian
> 
> Thank you! Here is the stack of a blocked `tail 0.txt` process:
> 
> cat /proc/276/stack
> [<0>] call_rwsem_down_read_failed+0x18/0x30
> [<0>] __percpu_down_read+0x58/0x80
> [<0>] __sb_start_write+0x65/0x70
> [<0>] xfs_trans_alloc+0xec/0x130 [xfs]
> [<0>] xfs_free_eofblocks+0x12a/0x1e0 [xfs]
> [<0>] xfs_release+0x144/0x170 [xfs]
> [<0>] xfs_file_release+0x15/0x20 [xfs]
> [<0>] __fput+0xea/0x220
> [<0>] ____fput+0xe/0x10
> [<0>] task_work_run+0x9d/0xc0
> [<0>] ptrace_notify+0x84/0x90
> [<0>] tracehook_report_syscall_exit+0x90/0xd0
> [<0>] syscall_slow_exit_work+0x50/0xd0
> [<0>] do_syscall_64+0x12b/0x130
> [<0>] entry_SYSCALL_64_after_hwframe+0x3d/0xa2
> [<0>] 0xffffffffffffffff
> 
> Your explanation matches the behaviour I see on the system.
> 
> If there was a patch, do you think it would get backported or just stay in
> mainline and ship with the regular releases?
> 

There was a patch, but it was RFC and hadn't been merged because IIRC
more investigation/testing was required to evaluate side effects. For
reference, the last post I see is the one below. In particular, patch 3
bypasses EOF block truncation from read-only file descriptors (I believe
the file writer task would still block).

https://marc.info/?l=linux-xfs&m=154951612101291&w=2

Based on the stack above, note that this is (at least for the time
being) expected behavior on XFS.

Brian

> Best,
> Stefan
> 
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