On 2011-03-11 09:06, Lukas Czerner wrote: > BZ29402 > https://bugzilla.kernel.org/show_bug.cgi?id=29402 > > We can hit serious mis-synchronization in bio completion path of > blkdev_issue_zeroout() leading to a panic. > > The problem is that when we are going to wait_for_completion() in > blkdev_issue_zeroout() we check if the bb.done equals issued (number of > submitted bios). If it does, we can skip the wait_for_completition() > and just out of the function since there is nothing to wait for. > However, there is a ordering problem because bio_batch_end_io() is > calling atomic_inc(&bb->done) before complete(), hence it might seem to > blkdev_issue_zeroout() that all bios has been completed and exit. At > this point when bio_batch_end_io() is going to call complete(bb->wait), > bb and wait does not longer exist since it was allocated on stack in > blkdev_issue_zeroout() ==> panic! > > (thread 1) (thread 2) > bio_batch_end_io() blkdev_issue_zeroout() > if(bb) { ... > if (bb->end_io) ... > bb->end_io(bio, err); ... > atomic_inc(&bb->done); ... > ... while (issued != atomic_read(&bb.done)) > ... (let issued == bb.done) > ... (do the rest of the function) > ... return ret; > complete(bb->wait); > ^^^^^^^^ > panic > > We can fix this easily by simplifying bio_batch and completion counting. > > Also remove bio_end_io_t *end_io since it is not used. Thanks Lukas, I'll expedite this for 2.6.38! -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
