Re: Spurious termination of fuse invalidation notifier thread

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Hi Raghavendra,

On 03/09/16 05:42, Raghavendra Gowdappa wrote:
Hi Xavi/Kaleb/Pranith,

During few of our older conversations (like [1], but not only one), some of you had reported that the thread which writes invalidation notifications (of inodes, entries) to /dev/fuse terminates spuriously. Csaba tried to reproduce the issue, but without success. It would be helpful if you provide any information on reproducer and/or possible reasons for the behavior.

I didn't found what really caused the problem. I only saw the termination message on a production server after some days working but hadn't had the opportunity to debug it.

Looking at the code, the only conclusion I got is that the result from the write to /dev/fuse was unexpected. The patch solves this and I haven't seen the problem again.

The old code only manages ENOENT error. It exits the thread for any other error. I guess that in some situations a write to /dev/fuse can return other "non fatal" errors.

As a guess, I think it may be a failure in an entry invalidation. Looking at the code of fuse, it may return ENOTDIR if parent of the entry is not a directory and some race happens doing rm/create while sending invalidations in the background. Another possibility is ENOTEMPTY if the entry references a non empty directory (again probably caused by races between user mode operations and background invalidations). Anyway this is only a guess, I have no more information.

Xavi


[1] http://review.gluster.org/#/c/13274/1/xlators/mount/fuse/src/fuse-bridge.c

regards,
Raghavendra

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