The patch titled Subject: nilfs2: fix potential bug in end_buffer_async_write has been added to the -mm mm-hotfixes-unstable branch. Its filename is nilfs2-fix-potential-bug-in-end_buffer_async_write.patch
This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...
This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------ From: Ryusuke Konishi konishi.ryusuke@gmail.com Subject: nilfs2: fix potential bug in end_buffer_async_write Date: Sun, 4 Feb 2024 01:16:45 +0900
According to a syzbot report, end_buffer_async_write(), which handles the completion of block device writes, may detect abnormal condition of the buffer async_write flag and cause a BUG_ON failure when using nilfs2.
Nilfs2 itself does not use end_buffer_async_write(). But, the async_write flag is now used as a marker by commit 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks") as a means of resolving double list insertion of dirty blocks in nilfs_lookup_dirty_data_buffers() and nilfs_lookup_node_buffers() and the resulting crash.
This modification is safe as long as it is used for file data and b-tree node blocks where the page caches are independent. However, it was irrelevant and redundant to also introduce async_write for segment summary and super root blocks that share buffers with the backing device. This led to the possibility that the BUG_ON check in end_buffer_async_write would fail as described above, if independent writebacks of the backing device occurred in parallel.
The use of async_write for segment summary buffers has already been removed in a previous change.
Fix this issue by removing the manipulation of the async_write flag for the remaining super root block buffer.
Link: https://lkml.kernel.org/r/20240203161645.4992-1-konishi.ryusuke@gmail.com Fixes: 7f42ec394156 ("nilfs2: fix issue with race condition of competition between segments for dirty blocks") Signed-off-by: Ryusuke Konishi konishi.ryusuke@gmail.com Reported-by: syzbot+5c04210f7c7f897c1e7f@syzkaller.appspotmail.com Closes: https://lkml.kernel.org/r/00000000000019a97c05fd42f8c8@google.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---
fs/nilfs2/segment.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
--- a/fs/nilfs2/segment.c~nilfs2-fix-potential-bug-in-end_buffer_async_write +++ a/fs/nilfs2/segment.c @@ -1703,7 +1703,6 @@ static void nilfs_segctor_prepare_write(
list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) { - set_buffer_async_write(bh); if (bh == segbuf->sb_super_root) { if (bh->b_folio != bd_folio) { folio_lock(bd_folio); @@ -1714,6 +1713,7 @@ static void nilfs_segctor_prepare_write( } break; } + set_buffer_async_write(bh); if (bh->b_folio != fs_folio) { nilfs_begin_folio_io(fs_folio); fs_folio = bh->b_folio; @@ -1800,7 +1800,6 @@ static void nilfs_abort_logs(struct list
list_for_each_entry(bh, &segbuf->sb_payload_buffers, b_assoc_buffers) { - clear_buffer_async_write(bh); if (bh == segbuf->sb_super_root) { clear_buffer_uptodate(bh); if (bh->b_folio != bd_folio) { @@ -1809,6 +1808,7 @@ static void nilfs_abort_logs(struct list } break; } + clear_buffer_async_write(bh); if (bh->b_folio != fs_folio) { nilfs_end_folio_io(fs_folio, err); fs_folio = bh->b_folio; @@ -1896,8 +1896,9 @@ static void nilfs_segctor_complete_write BIT(BH_Delay) | BIT(BH_NILFS_Volatile) | BIT(BH_NILFS_Redirected));
- set_mask_bits(&bh->b_state, clear_bits, set_bits); if (bh == segbuf->sb_super_root) { + set_buffer_uptodate(bh); + clear_buffer_dirty(bh); if (bh->b_folio != bd_folio) { folio_end_writeback(bd_folio); bd_folio = bh->b_folio; @@ -1905,6 +1906,7 @@ static void nilfs_segctor_complete_write update_sr = true; break; } + set_mask_bits(&bh->b_state, clear_bits, set_bits); if (bh->b_folio != fs_folio) { nilfs_end_folio_io(fs_folio, 0); fs_folio = bh->b_folio; _
Patches currently in -mm which might be from konishi.ryusuke@gmail.com are
nilfs2-fix-data-corruption-in-dsync-block-recovery-for-small-block-sizes.patch nilfs2-fix-hang-in-nilfs_lookup_dirty_data_buffers.patch nilfs2-fix-potential-bug-in-end_buffer_async_write.patch nilfs2-convert-segment-buffer-to-use-kmap_local.patch nilfs2-convert-nilfs_copy_buffer-to-use-kmap_local.patch nilfs2-convert-metadata-file-common-code-to-use-kmap_local.patch nilfs2-convert-sufile-to-use-kmap_local.patch nilfs2-convert-persistent-object-allocator-to-use-kmap_local.patch nilfs2-convert-dat-to-use-kmap_local.patch nilfs2-move-nilfs_bmap_write-call-out-of-nilfs_write_inode_common.patch nilfs2-do-not-acquire-rwsem-in-nilfs_bmap_write.patch nilfs2-convert-ifile-to-use-kmap_local.patch nilfs2-localize-highmem-mapping-for-checkpoint-creation-within-cpfile.patch nilfs2-localize-highmem-mapping-for-checkpoint-finalization-within-cpfile.patch nilfs2-localize-highmem-mapping-for-checkpoint-reading-within-cpfile.patch nilfs2-remove-nilfs_cpfile_getput_checkpoint.patch nilfs2-convert-cpfile-to-use-kmap_local.patch