On Thu, 10 Jan 2008 16:55:13 +0100 Jan Kara <[EMAIL PROTECTED]> wrote:
> Hi, > > sorry for the previous empty email... > > Supriya noted in his testing that sometimes buffers removed by > __remove_assoc_queue() don't have b_assoc_mapping set (and thus IO error > won't be properly propagated). Actually, looking more into the code I found > there are some more races. The patch below should fix them. It survived > beating with LTP and fsstress on ext2 filesystem on my testing machine so > it should be reasonably bugfree... Andrew, would you put the patch into > -mm? Thanks. > > Honza > -- > Jan Kara <[EMAIL PROTECTED]> > SUSE Labs, CR > --- > > There are two possible races in handling of private_list in buffer cache. > 1) When fsync_buffers_list() processes a private_list, it clears > b_assoc_mapping and moves buffer to its private list. Now drop_buffers() > comes, > sees a buffer is on list so it calls __remove_assoc_queue() which complains > about b_assoc_mapping being cleared (as it cannot propagate possible IO > error). > This race has been actually observed in the wild. private_lock should prevent this race. Which call to drop_buffers() is the culprit? The first one in try_to_free_buffers(), I assume? The "can this still happen?" one? If so, it can happen. How? Perhaps this is a bug. > 2) When fsync_buffers_list() processes a private_list, > mark_buffer_dirty_inode() can be called on bh which is already on the private > list of fsync_buffers_list(). As buffer is on some list (note that the check > is > performed without private_lock), it is not readded to the mapping's > private_list and after fsync_buffers_list() finishes, we have a dirty buffer > which should be on private_list but it isn't. This race has not been reported, > probably because most (but not all) callers of mark_buffer_dirty_inode() hold > i_mutex and thus are serialized with fsync(). Maybe fsync_buffers_list should put the buffer back onto private_list if it got dirtied again. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
