commit 38296afe3c6ee07319e01bb249aa4bb47c07b534 upstream. Syzbot reported a hang issue in migrate_pages_batch() called by mbind() and nilfs_lookup_dirty_data_buffers() called in the log writer of nilfs2. While migrate_pages_batch() locks a folio and waits for the writeback to complete, the log writer thread that should bring the writeback to completion picks up the folio being written back in nilfs_lookup_dirty_data_buffers() that it calls for subsequent log creation and was trying to lock the folio. Thus causing a deadlock. In the first place, it is unexpected that folios/pages in the middle of writeback will be updated and become dirty. Nilfs2 adds a checksum to verify the validity of the log being written and uses it for recovery at mount, so data changes during writeback are suppressed. Since this is broken, an unclean shutdown could potentially cause recovery to fail. Investigation revealed that the root cause is that the wait for writeback completion in nilfs_page_mkwrite() is conditional, and if the backing device does not require stable writes, data may be modified without waiting. Fix these issues by making nilfs_page_mkwrite() wait for writeback to finish regardless of the stable write requirement of the backing device. Link: https://lkml.kernel.org/r/20240131145657.4209-1-konishi.ryusuke@xxxxxxxxx Fixes: 1d1d1a767206 ("mm: only enforce stable page writes if the backing device requires it") Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Reported-by: syzbot+ee2ae68da3b22d04cd8d@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://lkml.kernel.org/r/00000000000047d819061004ad6c@xxxxxxxxxx Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Please apply this patch to the stable trees indicated by the subject line prefix. This patch is tailored to account for page/folio conversion and an fs-wide change around page_mkwrite, and is applicable as-is to all versions from v3.9 (where the issue was introduced) to v6.5. Also, all the builds and retests I did on each stable tree passed. Thanks, Ryusuke Konishi fs/nilfs2/file.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c index a265d391ffe9..822e8d95d31e 100644 --- a/fs/nilfs2/file.c +++ b/fs/nilfs2/file.c @@ -105,7 +105,13 @@ static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf) nilfs_transaction_commit(inode->i_sb); mapped: - wait_for_stable_page(page); + /* + * Since checksumming including data blocks is performed to determine + * the validity of the log to be written and used for recovery, it is + * necessary to wait for writeback to finish here, regardless of the + * stable write requirement of the backing device. + */ + wait_on_page_writeback(page); out: sb_end_pagefault(inode->i_sb); return block_page_mkwrite_return(ret); -- 2.39.3
