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From: David Howells <dhowells@redhat.com>
To: Dave Wysochanski <dwysocha@redhat.com>
Cc: dhowells@redhat.com, Daire Byrne <daire.byrne@gmail.com>,
	Benjamin Maynard <benmaynard@google.com>,
	linux-cachefs@redhat.com, linux-nfs@vger.kernel.org
Subject: Re: [PATCH 1/1] fscache: Fix oops due to race with cookie_lru and use_cookie
Date: Thu, 17 Nov 2022 13:30:37 +0000	[thread overview]
Message-ID: <3715748.1668691837@warthog.procyon.org.uk> (raw)
In-Reply-To: <20221117115023.1350181-2-dwysocha@redhat.com>

Dave Wysochanski <dwysocha@redhat.com> wrote:

> If a cookie expires from the LRU and the LRU_DISCARD flag is set,
> but the state machine has not run yet, it's possible another thread
> can call fscache_use_cookie and begin to use it.  When the
> cookie_worker finally runs, it will see the LRU_DISCARD flag set,
> transition the cookie->state to LRU_DISCARDING, which will then
> withdraw the cookie.  Once the cookie is withdrawn the object is
> removed the below oops will occur because the object associated
> with the cookie is now NULL.
> 
> Fix the oops by clearing the LRU_DISCARD bit if another thread
> uses the cookie before the cookie_worker runs.

I think this is the right approach.  The state machine should just fall
through without doing anything, despite having been woken.

David


  parent reply	other threads:[~2022-11-17 13:31 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-17 11:50 [PATCH 0/1] Fix oops in cachefiles_prepare_write due to cookie_lru and use_cookie race Dave Wysochanski
2022-11-17 11:50 ` [PATCH 1/1] fscache: Fix oops due to race with cookie_lru and use_cookie Dave Wysochanski
2022-11-17 13:30 ` David Howells [this message]
2022-11-17 13:36 ` David Howells
2022-11-17 13:52 ` David Howells
2022-11-17 14:10   ` David Wysochanski
2022-11-22  8:00 ` [PATCH 0/1] Fix oops in cachefiles_prepare_write due to cookie_lru and use_cookie race Daire Byrne

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