This is a note to let you know that I've just added the patch titled
nilfs2: fix hang in nilfs_lookup_dirty_data_buffers()
to the 4.19-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nilfs2-fix-hang-in-nilfs_lookup_dirty_data_buffers.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 38296afe3c6ee07319e01bb249aa4bb47c07b534 Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Date: Wed, 31 Jan 2024 23:56:57 +0900
Subject: nilfs2: fix hang in nilfs_lookup_dirty_data_buffers()
From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/nilfs2/file.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
--- a/fs/nilfs2/file.c
+++ b/fs/nilfs2/file.c
@@ -105,7 +105,13 @@ static vm_fault_t nilfs_page_mkwrite(str
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);
Patches currently in stable-queue which might be from konishi.ryusuke@xxxxxxxxx are
queue-4.19/nilfs2-fix-data-corruption-in-dsync-block-recovery-for-small-block-sizes.patch
queue-4.19/nilfs2-fix-hang-in-nilfs_lookup_dirty_data_buffers.patch
