diff options
Diffstat (limited to '0003-Btrfs-fix-unwritten-extent-buffers-and-hangs-on-future-writeback-attempts.patch')
| -rw-r--r-- | 0003-Btrfs-fix-unwritten-extent-buffers-and-hangs-on-future-writeback-attempts.patch | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/0003-Btrfs-fix-unwritten-extent-buffers-and-hangs-on-future-writeback-attempts.patch b/0003-Btrfs-fix-unwritten-extent-buffers-and-hangs-on-future-writeback-attempts.patch new file mode 100644 index 0000000..b6d19c3 --- /dev/null +++ b/0003-Btrfs-fix-unwritten-extent-buffers-and-hangs-on-future-writeback-attempts.patch @@ -0,0 +1,145 @@ +From 45fc8773f47b7cbe56caab0e14abf26d1e044e63 Mon Sep 17 00:00:00 2001 +From: Filipe Manana <fdmanana@suse.com> +Date: Wed, 11 Sep 2019 17:42:00 +0100 +Subject: Btrfs: fix unwritten extent buffers and hangs on future writeback + attempts + +The lock_extent_buffer_io() returns 1 to the caller to tell it everything +went fine and the callers needs to start writeback for the extent buffer +(submit a bio, etc), 0 to tell the caller everything went fine but it does +not need to start writeback for the extent buffer, and a negative value if +some error happened. + +When it's about to return 1 it tries to lock all pages, and if a try lock +on a page fails, and we didn't flush any existing bio in our "epd", it +calls flush_write_bio(epd) and overwrites the return value of 1 to 0 or +an error. The page might have been locked elsewhere, not with the goal +of starting writeback of the extent buffer, and even by some code other +than btrfs, like page migration for example, so it does not mean the +writeback of the extent buffer was already started by some other task, +so returning a 0 tells the caller (btree_write_cache_pages()) to not +start writeback for the extent buffer. Note that epd might currently have +either no bio, so flush_write_bio() returns 0 (success) or it might have +a bio for another extent buffer with a lower index (logical address). + +Since we return 0 with the EXTENT_BUFFER_WRITEBACK bit set on the +extent buffer and writeback is never started for the extent buffer, +future attempts to writeback the extent buffer will hang forever waiting +on that bit to be cleared, since it can only be cleared after writeback +completes. Such hang is reported with a trace like the following: + + [49887.347053] INFO: task btrfs-transacti:1752 blocked for more than 122 seconds. + [49887.347059] Not tainted 5.2.13-gentoo #2 + [49887.347060] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. + [49887.347062] btrfs-transacti D 0 1752 2 0x80004000 + [49887.347064] Call Trace: + [49887.347069] ? __schedule+0x265/0x830 + [49887.347071] ? bit_wait+0x50/0x50 + [49887.347072] ? bit_wait+0x50/0x50 + [49887.347074] schedule+0x24/0x90 + [49887.347075] io_schedule+0x3c/0x60 + [49887.347077] bit_wait_io+0x8/0x50 + [49887.347079] __wait_on_bit+0x6c/0x80 + [49887.347081] ? __lock_release.isra.29+0x155/0x2d0 + [49887.347083] out_of_line_wait_on_bit+0x7b/0x80 + [49887.347084] ? var_wake_function+0x20/0x20 + [49887.347087] lock_extent_buffer_for_io+0x28c/0x390 + [49887.347089] btree_write_cache_pages+0x18e/0x340 + [49887.347091] do_writepages+0x29/0xb0 + [49887.347093] ? kmem_cache_free+0x132/0x160 + [49887.347095] ? convert_extent_bit+0x544/0x680 + [49887.347097] filemap_fdatawrite_range+0x70/0x90 + [49887.347099] btrfs_write_marked_extents+0x53/0x120 + [49887.347100] btrfs_write_and_wait_transaction.isra.4+0x38/0xa0 + [49887.347102] btrfs_commit_transaction+0x6bb/0x990 + [49887.347103] ? start_transaction+0x33e/0x500 + [49887.347105] transaction_kthread+0x139/0x15c + +So fix this by not overwriting the return value (ret) with the result +from flush_write_bio(). We also need to clear the EXTENT_BUFFER_WRITEBACK +bit in case flush_write_bio() returns an error, otherwise it will hang +any future attempts to writeback the extent buffer, and undo all work +done before (set back EXTENT_BUFFER_DIRTY, etc). + +This is a regression introduced in the 5.2 kernel. + +Fixes: 2e3c25136adfb ("btrfs: extent_io: add proper error handling to lock_extent_buffer_for_io()") +Fixes: f4340622e0226 ("btrfs: extent_io: Move the BUG_ON() in flush_write_bio() one level up") +Reported-by: Zdenek Sojka <zsojka@seznam.cz> +Link: https://lore.kernel.org/linux-btrfs/GpO.2yos.3WGDOLpx6t%7D.1TUDYM@seznam.cz/T/#u +Reported-by: Stefan Priebe - Profihost AG <s.priebe@profihost.ag> +Link: https://lore.kernel.org/linux-btrfs/5c4688ac-10a7-fb07-70e8-c5d31a3fbb38@profihost.ag/T/#t +Reported-by: Drazen Kacar <drazen.kacar@oradian.com> +Link: https://lore.kernel.org/linux-btrfs/DB8PR03MB562876ECE2319B3E579590F799C80@DB8PR03MB5628.eurprd03.prod.outlook.com/ +Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204377 +Signed-off-by: Filipe Manana <fdmanana@suse.com> +--- + fs/btrfs/extent_io.c | 35 ++++++++++++++++++++++++++--------- + 1 file changed, 26 insertions(+), 9 deletions(-) + +diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c +index db337e53aab3..93900ff87df7 100644 +--- a/fs/btrfs/extent_io.c ++++ b/fs/btrfs/extent_io.c +@@ -3591,6 +3591,13 @@ void wait_on_extent_buffer_writeback(struct extent_buffer *eb) + TASK_UNINTERRUPTIBLE); + } + ++static void end_extent_buffer_writeback(struct extent_buffer *eb) ++{ ++ clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags); ++ smp_mb__after_atomic(); ++ wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK); ++} ++ + /* + * Lock eb pages and flush the bio if we can't the locks + * +@@ -3662,8 +3669,11 @@ static noinline_for_stack int lock_extent_buffer_for_io(struct extent_buffer *eb + + if (!trylock_page(p)) { + if (!flush) { +- ret = flush_write_bio(epd); +- if (ret < 0) { ++ int err; ++ ++ err = flush_write_bio(epd); ++ if (err < 0) { ++ ret = err; + failed_page_nr = i; + goto err_unlock; + } +@@ -3678,16 +3688,23 @@ err_unlock: + /* Unlock already locked pages */ + for (i = 0; i < failed_page_nr; i++) + unlock_page(eb->pages[i]); ++ /* ++ * Clear EXTENT_BUFFER_WRITEBACK and wake up anyone waiting on it. ++ * Also set back EXTENT_BUFFER_DIRTY so future attempts to this eb can ++ * be made and undo everything done before. ++ */ ++ btrfs_tree_lock(eb); ++ spin_lock(&eb->refs_lock); ++ set_bit(EXTENT_BUFFER_DIRTY, &eb->bflags); ++ end_extent_buffer_writeback(eb); ++ spin_unlock(&eb->refs_lock); ++ percpu_counter_add_batch(&fs_info->dirty_metadata_bytes, eb->len, ++ fs_info->dirty_metadata_batch); ++ btrfs_clear_header_flag(eb, BTRFS_HEADER_FLAG_WRITTEN); ++ btrfs_tree_unlock(eb); + return ret; + } + +-static void end_extent_buffer_writeback(struct extent_buffer *eb) +-{ +- clear_bit(EXTENT_BUFFER_WRITEBACK, &eb->bflags); +- smp_mb__after_atomic(); +- wake_up_bit(&eb->bflags, EXTENT_BUFFER_WRITEBACK); +-} +- + static void set_btree_ioerr(struct page *page) + { + struct extent_buffer *eb = (struct extent_buffer *)page->private; +-- +cgit v1.2.1-1-g437b + |