linux-kernel - Re: [2.6.38-3.x] [BUG] soft lockup - CPU#X stuck for 23s! (vfs, autofs, vserver)

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Message-ID: <CA+55aFymD=QGptAxjSEWffDSA94dtAjPjy-ox76fYWgHn9m+kA@mail.gmail.com>
Date:	Sun, 23 Sep 2012 18:10:30 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Paweł Sikora <pluto@...-linux.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	arekm@...-linux.org, baggins@...-linux.org
Subject: Re: [2.6.38-3.x] [BUG] soft lockup - CPU#X stuck for 23s! (vfs,
 autofs, vserver)

On Sat, Sep 22, 2012 at 11:09 PM, Paweł Sikora <pluto@...-linux.org> wrote:
>
>         br_read_lock(vfsmount_lock);

The vfsmount_lock is a "local-global" lock, where a read-lock is
rather cheap and takes just a per-cpu lock, but the downside is that a
write-lock is *very* expensive, and can cause serious trouble.

And the write lock is taken by the [un]mount() paths. Do *not* do
crazy things. If you do some insane "unmount and remount autofs" on a
1s granularity, you're doing insane things.

Why do you have that 1s timeout? Insane.

              Linus
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