linux-kernel - Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667]

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Date:	Mon, 26 May 2014 11:17:42 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Miklos Szeredi <mszeredi@...e.cz>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: fs/dcache.c - BUG: soft lockup - CPU#5 stuck for 22s! [systemd-udevd:1667]

On Mon, May 26, 2014 at 8:27 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
>
> That's the livelock.  OK.

Hmm. Is there any reason we don't have some exclusion around
"check_submounts_and_drop()"?

That would seem to be the simplest way to avoid any livelock: just
don't allow concurrent calls (we could make the lock per-filesystem or
whatever). This whole case should all be for just exceptional cases
anyway.

We already sleep in that thing (well, "cond_resched()"), so taking a
mutex should be fine.

The attached (TOTALLY UNTESTED!) patch as an example. Avert your eyes.
Mika, does this make any difference?

              Linus

View attachment "patch.diff" of type "text/plain" (637 bytes)