RE: [PATCH] ceph: add timeout protection to ceph_mdsc_sync() path

[Viacheslav Dubeyko]

On Wed, 2026-02-18 at 21:57 +0200, Ionut Nechita (Wind River) wrote:
> Hi Slava,
> 
> Thanks for testing and reproducing this with generic/013.
> 
> Looking at the stack trace you shared:
> 
>   ceph_mdsc_sync+0x4b4 -> wait_for_completion(&req->r_safe_completion)
>   ceph_sync_fs
>   sync_filesystem
>   __x64_sys_syncfs
> 
> This is the same pattern we see in the original report - the sync path
> blocks indefinitely on wait_for_completion() with no timeout. In your
> case it's ceph_mdsc_sync() hanging on r_safe_completion, which is
> exactly what patch 2/3 ("ceph: add timeout protection to
> ceph_mdsc_sync() path") addresses.
> 
> The root cause may differ from the original IPv6/EADDRNOTAVAIL scenario,
> but the symptom and the fix are the same - these wait_for_completion()
> calls in the sync path need timeout protection regardless of what causes
> the underlying delay.
> 
> All three patches are now also on LKML:
> 
>   1/3 - libceph: handle EADDRNOTAVAIL more gracefully (v2)
>   2/3 - ceph: add timeout protection to ceph_mdsc_sync() path
>   3/3 - ceph: add timeout protection to ceph_osdc_sync() path
> 
> I've also added more details and debug information to the Ceph tracker
> issue at https://urldefense.proofpoint.com/v2/url?u=https-3A__tracker.ceph.com_issues_74897&d=DwIDAg&c=BSDicqBQBDjDI9RkVyTcHQ&r=q5bIm4AXMzc8NJu1_RGmnQ2fMWKq4Y4RAkElvUgSs00&m=ty8gR4OjrwFXUQPjG9Dm4EapzO4Hwyj7aAX6INwulJY0GjoU0pTf7khYkXwrksDT&s=3fOX8o4od1TodhJw8SHCNjR4huXJS6VsRFYD6791DWM&e=  - it might help with
> your investigation.

Frankly speaking, I don't see the situation of blocked thread if I am adding
debug output. It looks like a race condition. And I am not sure now that adding
timeout is the proper fix. Probably, we have some issue that needs to be fixed
and timeout looks like workaround but not the fix. I don't think that I have the
IPv6/EADDRNOTAVAIL case on my side.

Thanks,
Slava.