From: Steven Rostedt <rostedt@goodmis.org>
To: Jeff Layton <jlayton@redhat.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
linux-cifs@vger.kernel.org, Steve French <sfrench@samba.org>,
Peter Zijlstra <peterz@infradead.org>,
Clark Williams <williams@redhat.com>,
"Luis Claudio R. Goncalves" <lclaudio@uudg.org>,
Thomas Gleixner <tglx@linutronix.de>, Tejun Heo <tj@kernel.org>,
uobergfe@redhat.com
Subject: Re: [RFC PATCH] cifs: Fix possible deadlock with cifs and work queues
Date: Thu, 20 Mar 2014 22:19:13 -0400 [thread overview]
Message-ID: <20140320221913.104b275d@gandalf.local.home> (raw)
In-Reply-To: <20140320195346.0876e175@tlielax.poochiereds.net>
On Thu, 20 Mar 2014 19:53:46 -0400
Jeff Layton <jlayton@redhat.com> wrote:
> Wait...why does the work running on CPU1 end up blocked on down_read()?
> Is it really getting stuck on the down_write you mention?
>
rwsems are fair locks. Readers will not block on a reader lock unless
there's a writer waiting. That's the key. As soon as a writer blocks on
a lock that is held by a reader (or multiple readers), new readers
coming in will also block to let the writer get a chance. Otherwise, it
is a unfair lock and the readers can starve the writer.
But people tend to forget that a waiting writer causes readers to block
on each other, and if the reader locks can deadlock each other, they
will deadlock with a writer waiting.
-- Steve
prev parent reply other threads:[~2014-03-21 2:19 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-03-19 19:12 Steven Rostedt
2014-03-19 19:34 ` Peter Zijlstra
2014-03-19 19:43 ` Steven Rostedt
2014-03-19 19:46 ` Steven Rostedt
2014-03-19 19:47 ` Peter Zijlstra
2014-03-19 20:28 ` Tejun Heo
2014-03-20 19:28 ` Jeffrey Layton
2014-03-20 20:57 ` Steven Rostedt
2014-03-20 21:02 ` Jeff Layton
2014-03-21 2:23 ` Steven Rostedt
2014-03-21 8:32 ` Pavel Shilovsky
2014-03-21 11:59 ` Jeff Layton
2014-03-21 12:17 ` Steven Rostedt
2014-03-21 12:41 ` Jeff Layton
2014-03-21 12:54 ` Steven Rostedt
2014-03-21 15:07 ` [PATCH v2] " Steven Rostedt
2014-03-23 5:57 ` Shirish Pargaonkar
2014-03-20 23:53 ` [RFC PATCH] " Jeff Layton
2014-03-21 2:19 ` Steven Rostedt [this message]
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