On Mon, Feb 12, 2024 at 03:46:15PM +1030, Qu Wenruo wrote: > [BUG] > There is a bug report that with zoned device and sectorsize is smaller > than page size (aka, subpage), btrfs would crash with a very basic > workload: > > # getconfig PAGESIZE > 16384 > # mkfs.btrfs -f $dev -s 4k > # mount $dev $mnt > # $fsstress -w -n 8 -s 1707820327 -v -d $mnt > # umount $mnt > > The crash would look like this (with CONFIG_BTRFS_ASSERT enabled): > > assertion failed: block_start != EXTENT_MAP_HOLE, in fs/btrfs/extent_io.c:1384 > ------------[ cut here ]------------ > kernel BUG at fs/btrfs/extent_io.c:1384! > CPU: 0 PID: 872 Comm: kworker/u9:2 Tainted: G OE 6.8.0-rc3-custom+ #7 > Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20231122-12.fc39 11/22/2023 > Workqueue: writeback wb_workfn (flush-btrfs-8) > pc : __extent_writepage_io+0x404/0x460 [btrfs] > lr : __extent_writepage_io+0x404/0x460 [btrfs] > Call trace: > __extent_writepage_io+0x404/0x460 [btrfs] > extent_write_locked_range+0x16c/0x460 [btrfs] > run_delalloc_cow+0x88/0x118 [btrfs] > btrfs_run_delalloc_range+0x128/0x228 [btrfs] > writepage_delalloc+0xb8/0x178 [btrfs] > __extent_writepage+0xc8/0x3a0 [btrfs] > extent_write_cache_pages+0x1cc/0x460 [btrfs] > extent_writepages+0x8c/0x120 [btrfs] > btrfs_writepages+0x18/0x30 [btrfs] > do_writepages+0x94/0x1f8 > __writeback_single_inode+0x4c/0x388 > writeback_sb_inodes+0x208/0x4b0 > wb_writeback+0x118/0x3c0 > wb_do_writeback+0xbc/0x388 > wb_workfn+0x80/0x240 > process_one_work+0x154/0x3c8 > worker_thread+0x2bc/0x3e0 > kthread+0xf4/0x108 > ret_from_fork+0x10/0x20 > Code: 9102c021 90000be0 91378000 9402bf53 (d4210000) > ---[ end trace 0000000000000000 ]--- > > [CAUSE] > There are several factors causing the problem: > > 1. __extent_writepage_io() requires all dirty ranges to have delalloc > executed > This can be solved by adding @start and @len parameter to only submit > IO for a subset of the page, and update several involved helpers to > do subpage checks. > > So this is not a big deal. > > 2. Subpage only accepts for full page aligned ranges for > extent_write_locked_range() > For zoned device, regular COW is switched to utilize > extent_write_locked_range() to submit the IO. > > But the caller, run_delalloc_cow() can be called to run on a subpage > range, e.g. > > 0 4K 8K 12K 16K > |/////| |/////| > > Where |///| is the dirtied range. > > In that case, btrfs_run_delalloc_range() would call run_delalloc_cow(), > which would call extent_write_locked_range() for [0, 4K), and unlock > the whole [0, 16K) page. > > But btrfs_run_delalloc_range() would again be called for range [8K, > 12K), as there are still dirty range left. > In that case, since the whole page is already unlocked by previous > iteration, and would cause different ASSERT()s inside > extent_write_locked_range(). > > That's also why compression for subpage cases require fully page > aligned range. > > [WORKAROUND] > A proper fix requires some big changes to delalloc workload, to allow > extent_write_locked_range() to handle multiple different entries with > the same @locked_page. > > So for now, disable read-write support for subpage zoned btrfs. > > The problem can only be solved if subpage btrfs can handle subpage > compression, which need quite some work on the delalloc procedure for > the @locked_page handling. > > Reported-by: HAN Yuwei <hrx@xxxxxxxx> > Link: https://lore.kernel.org/all/1ACD2E3643008A17+da260584-2c7f-432a-9e22-9d390aae84cc@xxxxxxxx/ > CC: stable@xxxxxxxxxxxxxxx # 5.10+ > Signed-off-by: Qu Wenruo <wqu@xxxxxxxx> > --- > fs/btrfs/disk-io.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c > index c3ab268533ca..85cd23aebdd6 100644 > --- a/fs/btrfs/disk-io.c > +++ b/fs/btrfs/disk-io.c > @@ -3193,7 +3193,8 @@ int btrfs_check_features(struct btrfs_fs_info *fs_info, bool is_rw_mount) > * part of @locked_page. > * That's also why compression for subpage only work for page aligned ranges. > */ > - if (fs_info->sectorsize < PAGE_SIZE && btrfs_is_zoned(fs_info) && is_rw_mount) { > + if (fs_info->sectorsize < PAGE_SIZE && > + btrfs_fs_incompat(fs_info, ZONED) && is_rw_mount) { > btrfs_warn(fs_info, > "no zoned read-write support for page size %lu with sectorsize %u", > PAGE_SIZE, fs_info->sectorsize); This does not match any code I see in usual branches and it also does not apply so it can't be picked as a fix.
