+41
−39
Loading
xfs: use sync buffer I/O for sync delwri queue submission
If a delwri queue occurs of a buffer that sits on a delwri queue wait list, the queue sets _XBF_DELWRI_Q without changing the state of ->b_list. This occurs, for example, if another thread beats the current delwri waiter thread to the buffer lock after I/O completion. Once the waiter acquires the lock, it removes the buffer from the wait list and leaves a buffer with _XBF_DELWRI_Q set but not populated on a list. This results in a lost buffer submission and in turn can result in assert failures due to _XBF_DELWRI_Q being set on buffer reclaim or filesystem lockups if the buffer happens to cover an item in the AIL. This problem has been reproduced by repeated iterations of xfs/305 on high CPU count (28xcpu) systems with limited memory (~1GB). Dirty dquot reclaim races with an xfsaild push of a separate dquot backed by the same buffer such that the buffer sits on the reclaim wait list at the time xfsaild attempts to queue it. Since the latter dquot has been flush locked but the underlying buffer not submitted for I/O, the dquot pins the AIL and causes the filesystem to livelock. This race is essentially made possible by the buffer lock cycle involved with waiting on a synchronous delwri queue submission. Close the race by using synchronous buffer I/O for respective delwri queue submission. This means the buffer remains locked across the I/O and so is inaccessible from other contexts while in the intermediate wait list state. The sync buffer I/O wait mechanism is factored into a helper such that sync delwri buffer submission and serialization are batched operations. Designed-by:Dave Chinner <dchinner@redhat.com> Signed-off-by: