From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?utf-8?B?UGF3ZcWC?= Sikora <pluto@pld-linux.org>
Subject: Re: [2.6.38-3.x] [BUG] soft lockup - CPU#X stuck for 23s! (vfs, autofs, vserver)
Date: Mon, 24 Sep 2012 07:23:55 +0200
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References: <5092540.GORQ1kUuNX@localhost> <CA+55aFymD=QGptAxjSEWffDSA94dtAjPjy-ox76fYWgHn9m+kA@mail.gmail.com>
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Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	arekm@pld-linux.org, baggins@pld-linux.org, herbert@13thfloor.at
To: Linus Torvalds <torvalds@linux-foundation.org>
Return-path: <linux-kernel-owner@vger.kernel.org>
In-Reply-To: <CA+55aFymD=QGptAxjSEWffDSA94dtAjPjy-ox76fYWgHn9m+kA@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
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On Sunday 23 of September 2012 18:10:30 Linus Torvalds wrote:
> On Sat, Sep 22, 2012 at 11:09 PM, Pawe=C5=82 Sikora <pluto@pld-linux.=
org> wrote:
> >
> >         br_read_lock(vfsmount_lock);
>=20
> 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.
>=20
> 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.
>=20
> Why do you have that 1s timeout? Insane.

1s unmount timeout is *only* for fast bug reproduction (in few seconds =
after opteron startup)
and testing potential patches. normally with 60s timeout it happens in =
few minutes..hours
(depends on machine i/o+cpu load) and makes server unusable (permament =
soft-lockup).
can we redesign vserver's mnt_is_reachable() for better locking to avoi=
d total soft-lockup?

BR,
Pawe=C5=82.

ps).
i'm adding Herbert to CC.