On Wed, 7 Dec 2011 13:11:58 +0200, Ilya Dryomov wrote: > On Wed, Dec 07, 2011 at 10:31:35AM +0800, Miao Xie wrote: >> On tue, 6 Dec 2011 16:36:11 -0500, Chris Mason wrote: >>> On Tue, Dec 06, 2011 at 06:23:23AM -0500, Christoph Hellwig wrote: >>>> On Tue, Dec 06, 2011 at 07:06:40PM +0800, Miao Xie wrote: >>>>>> I can't see why you need the writeout when the trylocks fails. Umount >>>>>> needs to take care of writing out all pending file data anyway, so doing >>>>>> it from the cleaner thread in addition doesn't sound like it would help. >>>>> >>>>> umount invokes sync_fs() and write out all the dirty file data. For the >>>>> other file systems, its OK because the file system does not introduce dirty pages >>>>> by itself. But btrfs is different. Its automatic defragment will make lots of dirty >>>>> pages after sync_fs() and reserve lots of meta-data space for those pages. >>>>> And then the cleaner thread may find there is no enough space to reserve, it must >>>>> sync the dirty file data and release the reserved space which is for the dirty >>>>> file data. >>>> >>>> I think the safest way to fix is is to write out all dirty data again >>>> once the cleaner thread has been safely stopped. >>>> >>> >>> Said another way we want to stop the autodefrag code before the unmount >>> is ready to continue. We also want to stop balancing, scrub etc. >> >> But there is no good interface to do it before umount gets s_umount lock. >> I think trylock(in writeback_inodes_sb_nr_if_idle()) + dirty data flush >> can help us to fix the bug perfectly. > > But it won't fix the umount while balancing family of deadlocks (they > are really of the same nature, vfs grabs s_umount mutex and we need it > to proceed). (Balance cancelling code is part of restriper patches, > it's just a hook in close_ctree() that waits until we are done > relocating a chunk - very similar to cleaner wait) I will change the logic, we will add a while loop to check if something is running(xxx_running is not zero), if yes, invoke btrfs_sync_fs() to do dirty page flush. > > One example would be that balancing code while dirtying pages calls > balance_dirty_pages_ratelimited() for each dirtied page, as it should. > And if balance_dirty_pages() then decides to initiate writeback we are > stuck schedule()ing forever, because writeback can't proceed w/o > read-taking s_umount mutex which is fully held by vfs - it just skips > the relocation inode. AFAIK, balance_dirty_pages() just wake up the flush thread, and the flush thread also doesn't grab s_umount. So we needn't worry about it.I think. Thanks Miao -- 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
