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From: Patrick McHardy <kaber@trash.net>
To: Linux Netdev List <netdev@vger.kernel.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Subject: IPv4/IPv6 sysctl unregistration deadlock
Date: Wed, 25 Feb 2009 06:23:33 +0100	[thread overview]
Message-ID: <49A4D5D5.5090602@trash.net> (raw)

Ben Greear reported sporadically hanging ip processes when adding or
removing MACVLAN devices, which seem to be caused by a race between
sysctl handling and device notifiers.

What is happening is:

Process 1:

- "ip" deletes a macvlan device (or any other kind of device gets
   removed for whatever reason)
- netdev notifier chain notifies IPv6 addrconf while holding the RTNL

Process 2:

- a different process writes something to /proc/sys/net/ipv6/forwarding
- sysctl table is marked as busy, addrconf_sysctl_forward() is invoked
- tries to take rtnl, waits for process 1

Process 1:

- IPv6 begins sysctl unregistration, which is deferred using a
   completion until the table is not busy anymore (=> waiting for
   process 2)

At this point both processes are deadlocked. Judging by a quick look,
IPv4 seems to have the exact same problem.

An easy fix would be to keep track of whether sysctl unregistration
is in progress in IPv4/IPv6 and ignore new requests from that point
on. Its not very elegant though, so I was wondering whether anyone
has a better suggestion.


             reply	other threads:[~2009-02-25  5:23 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2009-02-25  5:23 Patrick McHardy [this message]
2009-02-25  6:19 ` IPv4/IPv6 sysctl unregistration deadlock Herbert Xu
2009-02-25  6:23   ` Patrick McHardy
2009-02-25  7:18     ` Patrick McHardy
2009-02-25  8:43       ` Herbert Xu
2009-02-26  6:06         ` Eric W. Biederman
2009-02-26  6:10         ` Eric W. Biederman
2009-02-26  6:22           ` Herbert Xu
2009-02-26  7:18             ` Eric W. Biederman
2009-02-26 16:49               ` Stephen Hemminger
2009-02-26 19:01                 ` Eric W. Biederman
2009-02-26 20:24                   ` Stephen Hemminger
2009-02-27  0:59                 ` Herbert Xu
2009-02-27  1:25                   ` Stephen Hemminger
2009-02-27 18:26                 ` Ben Greear
2009-02-27 18:38                   ` Stephen Hemminger
2009-03-02 11:07                     ` Patrick McHardy
2009-03-02 11:21                       ` Patrick McHardy
2009-03-02 22:11                     ` Ben Greear
2009-03-02 22:20                       ` Patrick McHardy
2009-03-02 22:47                         ` David Miller
2009-03-02 23:03                           ` Patrick McHardy
2009-03-03  8:48                             ` David Miller
2009-03-08  3:36                               ` Eric W. Biederman
2009-02-26 16:55       ` Stephen Hemminger

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