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| author | Eric Dumazet <eric.dumazet@gmail.com> | 2013-05-01 05:24:03 +0000 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2015-12-30 02:26:03 +0000 |
| commit | 2ee9cbe7e7bfe2d36374288b818aa31b2c4981db (patch) | |
| tree | b5d67e66fd1d32fc971805621825914f70f3b182 /include | |
| parent | 1a3b55eee77490693bb4d1338f24b6c9f11e3e1d (diff) | |
| download | lwn-2ee9cbe7e7bfe2d36374288b818aa31b2c4981db.tar.gz lwn-2ee9cbe7e7bfe2d36374288b818aa31b2c4981db.zip | |
af_unix: fix a fatal race with bit fields
commit 60bc851ae59bfe99be6ee89d6bc50008c85ec75d upstream.
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 <ambrose@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/net/af_unix.h | 5 |
1 files changed, 3 insertions, 2 deletions
diff --git a/include/net/af_unix.h b/include/net/af_unix.h index 9ad39fa59d92..f4842f7afaa5 100644 --- a/include/net/af_unix.h +++ b/include/net/af_unix.h @@ -54,9 +54,10 @@ 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; wait_queue_t peer_wake; }; |