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Message-ID: <49A4D5D5.5090602@trash.net> Date: Wed, 25 Feb 2009 06:23:33 +0100 From: Patrick McHardy <kaber@...sh.net> To: Linux Netdev List <netdev@...r.kernel.org> CC: Herbert Xu <herbert@...dor.apana.org.au> Subject: IPv4/IPv6 sysctl unregistration deadlock 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. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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