From: Eric Dumazet Date: Wed, 1 May 2013 05:24:03 +0000 (+0000) Subject: af_unix: fix a fatal race with bit fields X-Git-Tag: omap-for-v3.10/dt-fixes-for-merge-window~77^2~1 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=60bc851ae59bfe99be6ee89d6bc50008c85ec75d;p=pandora-kernel.git af_unix: fix a fatal race with bit fields Using bit fields is dangerous on ppc64/sparc64, as the compiler [1] uses 64bit instructions to manipulate them. If the 64bit word includes any atomic_t or spinlock_t, we can lose critical concurrent changes. This is happening in af_unix, where unix_sk(sk)->gc_candidate/ gc_maybe_cycle/lock share the same 64bit word. This leads to fatal deadlock, as one/several cpus spin forever on a spinlock that will never be available again. A safer way would be to use a long to store flags. This way we are sure compiler/arch wont do bad things. As we own unix_gc_lock spinlock when clearing or setting bits, we can use the non atomic __set_bit()/__clear_bit(). recursion_level can share the same 64bit location with the spinlock, as it is set only with this spinlock held. [1] bug fixed in gcc-4.8.0 : http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52080 Reported-by: Ambrose Feinstein Signed-off-by: Eric Dumazet Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Signed-off-by: David S. Miller --- Reading git-diff-tree failed