On Sun, Jan 01, 2017 at 11:13:06AM +0300, Christoph Hellwig wrote: > There is a race window between write_cache_pages calling > clear_page_dirty_for_io and XFS calling set_page_writeback, in which > the mapping for an inode is tagged neither as dirty, nor as writeback. > > If the COW shrinker hits in exactly that window we'll remove the delayed > COW extents and writepages trying to write it back, which in release > kernels will manifest as corruption of the bmap btree, and in debug > kernels will trip the ASSERT about now calling xfs_bmapi_write with the > COWFORK flag for holes. A complex customer load manages to hit this > window fairly reliably, probably by always having COW writeback in flight > while the cow shrinker runs. > > This patch adds another check for having the I_DIRTY_PAGES flag set, > which is still set during this race window. While this fixes the problem > I'm still not overly happy about the way the COW shrinker works as it > still seems a bit fragile. > > Signed-off-by: Christoph Hellwig <hch@xxxxxx> > --- > fs/xfs/xfs_icache.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/xfs/xfs_icache.c b/fs/xfs/xfs_icache.c > index f295049..2d5a63a 100644 > --- a/fs/xfs/xfs_icache.c > +++ b/fs/xfs/xfs_icache.c > @@ -1593,7 +1593,8 @@ xfs_inode_free_cowblocks( > * If the mapping is dirty or under writeback we cannot touch the > * CoW fork. Leave it alone if we're in the midst of a directio. > */ > - if (mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_DIRTY) || > + if ((VFS_I(ip)->i_state & I_DIRTY_PAGES) || > + mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_DIRTY) || > mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_WRITEBACK) || > atomic_read(&VFS_I(ip)->i_dio_count)) > return 0; Applied, thx. --D > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
