Currently unlock_buffer() contains a smb_mb__after_clear_bit() which is weird because bit_spin_unlock() uses smb_mb__before_clear_bit(): >From include/linux/bit_spinlock.h: static inline void bit_spin_unlock(int bitnum, unsigned long *addr) { smp_mb__before_clear_bit(); clear_bit(bitnum, addr); preempt_enable(); __release(bitlock); } For most architectures there is no difference because both smp_mb__after_clear_bit() and smp_mb__before_clear_bit() are both memory barriers and clear_buffer_locked() is an atomic operation. However, they differ under IA64. Note that this potential race has never been seen under IA64. It was discovered by inspection by Zoltan Menyhart <Zoltan.Menyhart@xxxxxxx>. Regardless if this is a true race or not, I think the unlock sequence needs to be the same for bit locks and unlock_buffer(). Maybe unlock_buffer and lock_buffer better use bit spinlock operations? Change unlock_buffer() to work the same way as bit_spin_unlock. Signed-off-by: Christoph Lameter <clameter@xxxxxxx> Index: linux-2.6/fs/buffer.c =================================================================== --- linux-2.6.orig/fs/buffer.c 2006-03-27 14:09:54.000000000 -0800 +++ linux-2.6/fs/buffer.c 2006-03-27 19:40:32.000000000 -0800 @@ -78,8 +78,8 @@ EXPORT_SYMBOL(__lock_buffer); void fastcall unlock_buffer(struct buffer_head *bh) { + smp_mb__before_clear_bit(); clear_buffer_locked(bh); - smp_mb__after_clear_bit(); wake_up_bit(&bh->b_state, BH_Lock); } - : send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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