From: Marcel Holtmann <marcel@holtmann•org>
To: Patrick McHardy <kaber@trash•net>
Cc: Jarek Poplawski <jarkao2@gmail•com>,
netdev@vger•kernel.org, Ingo Molnar <mingo@elte•hu>,
Thomas Graf <tgraf@suug•ch>
Subject: Re: netlink circular locking dependency
Date: Tue, 17 Jun 2008 03:45:54 +0200 [thread overview]
Message-ID: <1213667154.21932.47.camel@violet.holtmann.net> (raw)
In-Reply-To: <4856DF91.30606@trash.net>
Hi Patrick,
> >> =======================================================
> >> [ INFO: possible circular locking dependency detected ]
> >> 2.6.26-rc2 #5
> >> -------------------------------------------------------
> >> hcid/4136 is trying to acquire lock:
> >> (genl_mutex){--..}, at: [<c0000000002ace4c>] .ctrl_dumpfamily+0x74/0x174
> >>
> >> but task is already holding lock:
> >> (nlk->cb_mutex){--..}, at: [<c0000000002a766c>] .netlink_dump+0x58/0x27c
> >>
> >> which lock already depends on the new lock.
> >>
> > ...
> >
> > Hi,
> >
> > IMHO it looks like a real lockup threat. Probably it needs something
> > better, but for now here is my simplistic patch proposal for testing.
> >
> So we have:
>
> genl_rcv() : take genl_mutex
> genl_rcv_msg() : call netlink_dump_start() while holding genl_mutex
> netlink_dump_start(),
> netlink_dump() : take nlk->cb_mutex
> ctrl_dumpfamily() : try to detect this case and not take genl_mutex a
> second time
>
> netlink_rcv() : call netlink_dump
> netlink_dump : take nlk->cb_mutex
> ctrl_dumpfamily() : take genl_mutex
>
> which is a real bug.
>
> It seems the best fix is to use genl_mutex for the netlink cb_mutex,
> drop genl_mutex before calling netlink_dump_start and don't take it
> in ctrl_dumpfamily, relying completely on af_netlink.c for dump
> locking. Unfortunately this creates a race since the ops passed to
> netlink_dump_start are also protect by the mutex, so this patch
> is just for testing whether it fixes the warning.
I updated my test kernel to 2.6.26-rc6 and then applied your patch and
the lockdep warning goes away.
Regards
Marcel
next prev parent reply other threads:[~2008-06-17 1:42 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-14 12:35 netlink circular locking dependency Marcel Holtmann
2008-06-16 21:34 ` Jarek Poplawski
2008-06-16 21:48 ` Patrick McHardy
2008-06-17 1:45 ` Marcel Holtmann [this message]
2008-06-17 12:50 ` Patrick McHardy
2008-06-17 13:09 ` Jarek Poplawski
2008-06-17 13:07 ` Patrick McHardy
2008-06-17 13:24 ` Jarek Poplawski
2008-06-17 13:27 ` Patrick McHardy
2008-06-17 13:43 ` Jarek Poplawski
2008-06-18 4:30 ` David Miller
2008-06-18 6:15 ` Jarek Poplawski
2008-06-18 8:52 ` Patrick McHardy
2008-06-18 9:08 ` David Miller
2008-06-18 11:38 ` Marcel Holtmann
2008-06-18 11:42 ` Patrick McHardy
2008-06-17 13:08 ` Thomas Graf
2008-06-17 13:19 ` Patrick McHardy
2008-06-17 8:49 ` Jarek Poplawski
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