From: Naohiro Aota naohiro.aota@wdc.com
[ Upstream commit 9ce7466f372d83054c7494f6b3e4b9abaf3f0355 ]
There is a hung_task report on zoned btrfs like below.
https://github.com/naota/linux/issues/59
[726.328648] INFO: task rocksdb:high0:11085 blocked for more than 241 seconds. [726.329839] Not tainted 5.16.0-rc1+ #1 [726.330484] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [726.331603] task:rocksdb:high0 state:D stack: 0 pid:11085 ppid: 11082 flags:0x00000000 [726.331608] Call Trace: [726.331611] <TASK> [726.331614] __schedule+0x2e5/0x9d0 [726.331622] schedule+0x58/0xd0 [726.331626] io_schedule+0x3f/0x70 [726.331629] __folio_lock+0x125/0x200 [726.331634] ? find_get_entries+0x1bc/0x240 [726.331638] ? filemap_invalidate_unlock_two+0x40/0x40 [726.331642] truncate_inode_pages_range+0x5b2/0x770 [726.331649] truncate_inode_pages_final+0x44/0x50 [726.331653] btrfs_evict_inode+0x67/0x480 [726.331658] evict+0xd0/0x180 [726.331661] iput+0x13f/0x200 [726.331664] do_unlinkat+0x1c0/0x2b0 [726.331668] __x64_sys_unlink+0x23/0x30 [726.331670] do_syscall_64+0x3b/0xc0 [726.331674] entry_SYSCALL_64_after_hwframe+0x44/0xae [726.331677] RIP: 0033:0x7fb9490a171b [726.331681] RSP: 002b:00007fb943ffac68 EFLAGS: 00000246 ORIG_RAX: 0000000000000057 [726.331684] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb9490a171b [726.331686] RDX: 00007fb943ffb040 RSI: 000055a6bbe6ec20 RDI: 00007fb94400d300 [726.331687] RBP: 00007fb943ffad00 R08: 0000000000000000 R09: 0000000000000000 [726.331688] R10: 0000000000000031 R11: 0000000000000246 R12: 00007fb943ffb000 [726.331690] R13: 00007fb943ffb040 R14: 0000000000000000 R15: 00007fb943ffd260 [726.331693] </TASK>
While we debug the issue, we found running fstests generic/551 on 5GB non-zoned null_blk device in the emulated zoned mode also had a similar hung issue.
Also, we can reproduce the same symptom with an error injected cow_file_range() setup.
The hang occurs when cow_file_range() fails in the middle of allocation. cow_file_range() called from do_allocation_zoned() can split the give region ([start, end]) for allocation depending on current block group usages. When btrfs can allocate bytes for one part of the split regions but fails for the other region (e.g. because of -ENOSPC), we return the error leaving the pages in the succeeded regions locked. Technically, this occurs only when @unlock == 0. Otherwise, we unlock the pages in an allocated region after creating an ordered extent.
Considering the callers of cow_file_range(unlock=0) won't write out the pages, we can unlock the pages on error exit from cow_file_range(). So, we can ensure all the pages except @locked_page are unlocked on error case.
In summary, cow_file_range now behaves like this:
- page_started == 1 (return value) - All the pages are unlocked. IO is started. - unlock == 1 - All the pages except @locked_page are unlocked in any case - unlock == 0 - On success, all the pages are locked for writing out them - On failure, all the pages except @locked_page are unlocked
Fixes: 42c011000963 ("btrfs: zoned: introduce dedicated data write path for zoned filesystems") CC: stable@vger.kernel.org # 5.12+ Reviewed-by: Filipe Manana fdmanana@suse.com Signed-off-by: Naohiro Aota naohiro.aota@wdc.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/inode.c | 72 ++++++++++++++++++++++++++++++++++++++++++------ 1 file changed, 64 insertions(+), 8 deletions(-)
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 1b4fee8a2f28..20d0dea1d0c4 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -1053,6 +1053,28 @@ static u64 get_extent_allocation_hint(struct btrfs_inode *inode, u64 start, * *page_started is set to one if we unlock locked_page and do everything * required to start IO on it. It may be clean and already done with * IO when we return. + * + * When unlock == 1, we unlock the pages in successfully allocated regions. + * When unlock == 0, we leave them locked for writing them out. + * + * However, we unlock all the pages except @locked_page in case of failure. + * + * In summary, page locking state will be as follow: + * + * - page_started == 1 (return value) + * - All the pages are unlocked. IO is started. + * - Note that this can happen only on success + * - unlock == 1 + * - All the pages except @locked_page are unlocked in any case + * - unlock == 0 + * - On success, all the pages are locked for writing out them + * - On failure, all the pages except @locked_page are unlocked + * + * When a failure happens in the second or later iteration of the + * while-loop, the ordered extents created in previous iterations are kept + * intact. So, the caller must clean them up by calling + * btrfs_cleanup_ordered_extents(). See btrfs_run_delalloc_range() for + * example. */ static noinline int cow_file_range(struct btrfs_inode *inode, struct page *locked_page, @@ -1062,6 +1084,7 @@ static noinline int cow_file_range(struct btrfs_inode *inode, struct btrfs_root *root = inode->root; struct btrfs_fs_info *fs_info = root->fs_info; u64 alloc_hint = 0; + u64 orig_start = start; u64 num_bytes; unsigned long ram_size; u64 cur_alloc_size = 0; @@ -1245,18 +1268,44 @@ static noinline int cow_file_range(struct btrfs_inode *inode, btrfs_dec_block_group_reservations(fs_info, ins.objectid); btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 1); out_unlock: + /* + * Now, we have three regions to clean up: + * + * |-------(1)----|---(2)---|-------------(3)----------| + * `- orig_start `- start `- start + cur_alloc_size `- end + * + * We process each region below. + */ + clear_bits = EXTENT_LOCKED | EXTENT_DELALLOC | EXTENT_DELALLOC_NEW | EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV; page_ops = PAGE_UNLOCK | PAGE_START_WRITEBACK | PAGE_END_WRITEBACK; + /* - * If we reserved an extent for our delalloc range (or a subrange) and - * failed to create the respective ordered extent, then it means that - * when we reserved the extent we decremented the extent's size from - * the data space_info's bytes_may_use counter and incremented the - * space_info's bytes_reserved counter by the same amount. We must make - * sure extent_clear_unlock_delalloc() does not try to decrement again - * the data space_info's bytes_may_use counter, therefore we do not pass - * it the flag EXTENT_CLEAR_DATA_RESV. + * For the range (1). We have already instantiated the ordered extents + * for this region. They are cleaned up by + * btrfs_cleanup_ordered_extents() in e.g, + * btrfs_run_delalloc_range(). EXTENT_LOCKED | EXTENT_DELALLOC are + * already cleared in the above loop. And, EXTENT_DELALLOC_NEW | + * EXTENT_DEFRAG | EXTENT_CLEAR_META_RESV are handled by the cleanup + * function. + * + * However, in case of unlock == 0, we still need to unlock the pages + * (except @locked_page) to ensure all the pages are unlocked. + */ + if (!unlock && orig_start < start) + extent_clear_unlock_delalloc(inode, orig_start, start - 1, + locked_page, 0, page_ops); + + /* + * For the range (2). If we reserved an extent for our delalloc range + * (or a subrange) and failed to create the respective ordered extent, + * then it means that when we reserved the extent we decremented the + * extent's size from the data space_info's bytes_may_use counter and + * incremented the space_info's bytes_reserved counter by the same + * amount. We must make sure extent_clear_unlock_delalloc() does not try + * to decrement again the data space_info's bytes_may_use counter, + * therefore we do not pass it the flag EXTENT_CLEAR_DATA_RESV. */ if (extent_reserved) { extent_clear_unlock_delalloc(inode, start, @@ -1268,6 +1317,13 @@ static noinline int cow_file_range(struct btrfs_inode *inode, if (start >= end) goto out; } + + /* + * For the range (3). We never touched the region. In addition to the + * clear_bits above, we add EXTENT_CLEAR_DATA_RESV to release the data + * space_info's bytes_may_use counter, reserved in + * btrfs_check_data_free_space(). + */ extent_clear_unlock_delalloc(inode, start, end, locked_page, clear_bits | EXTENT_CLEAR_DATA_RESV, page_ops);