From 60bc851ae59bfe99be6ee89d6bc50008c85ec75d Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 1 May 2013 05:24:03 +0000 Subject: 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 --- include/net/af_unix.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'include/net/af_unix.h') diff --git a/include/net/af_unix.h b/include/net/af_unix.h index a8836e8445cc..dbdfd2b0f3b3 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -57,9 +57,10 @@ struct unix_sock { struct list_head link; atomic_long_t inflight; spinlock_t lock; - unsigned int gc_candidate : 1; - unsigned int gc_maybe_cycle : 1; unsigned char recursion_level; + unsigned long gc_flags; +#define UNIX_GC_CANDIDATE 0 +#define UNIX_GC_MAYBE_CYCLE 1 struct socket_wq peer_wq; }; #define unix_sk(__sk) ((struct unix_sock *)__sk) -- cgit v1.2.3-59-g8ed1b