• Eric Dumazet's avatar
    af_unix: fix a fatal race with bit fields · 60bc851a
    Eric Dumazet authored
    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=52080Reported-by: default avatarAmbrose Feinstein <ambrose@google.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Cc: Paul Mackerras <paulus@samba.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    60bc851a
garbage.c 10.5 KB