The patch titled
Subject: nilfs2: fix potential kernel bug due to lack of writeback flag waiting
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
nilfs2-fix-potential-kernel-bug-due-to-lack-of-writeback-flag-waiting.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/nilfs2-fix-potential-kernel-bug-due-to-lack-of-writeback-flag-waiting.patch
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@xxxxxxxxx>
Subject: nilfs2: fix potential kernel bug due to lack of writeback flag waiting
Date: Thu, 30 May 2024 23:15:56 +0900
Destructive writes to a block device on which nilfs2 is mounted can cause
a kernel bug in the folio/page writeback start routine or writeback end
routine (__folio_start_writeback in the log below):
kernel BUG at mm/page-writeback.c:3070!
Oops: invalid opcode: 0000 [#1] PREEMPT SMP KASAN PTI
...
RIP: 0010:__folio_start_writeback+0xbaa/0x10e0
Code: 25 ff 0f 00 00 0f 84 18 01 00 00 e8 40 ca c6 ff e9 17 f6 ff ff
e8 36 ca c6 ff 4c 89 f7 48 c7 c6 80 c0 12 84 e8 e7 b3 0f 00 90 <0f>
0b e8 1f ca c6 ff 4c 89 f7 48 c7 c6 a0 c6 12 84 e8 d0 b3 0f 00
...
Call Trace:
<TASK>
nilfs_segctor_do_construct+0x4654/0x69d0 [nilfs2]
nilfs_segctor_construct+0x181/0x6b0 [nilfs2]
nilfs_segctor_thread+0x548/0x11c0 [nilfs2]
kthread+0x2f0/0x390
ret_from_fork+0x4b/0x80
ret_from_fork_asm+0x1a/0x30
</TASK>
This is because when the log writer starts a writeback for segment summary
blocks or a super root block that use the backing device's page cache, it
does not wait for the ongoing folio/page writeback, resulting in an
inconsistent writeback state.
Fix this issue by waiting for ongoing writebacks when putting
folios/pages on the backing device into writeback state.
Link: https://lkml.kernel.org/r/20240530141556.4411-1-konishi.ryusuke@xxxxxxxxx
Fixes: 9ff05123e3bf ("nilfs2: segment constructor")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/nilfs2/segment.c | 3 +++
1 file changed, 3 insertions(+)
--- a/fs/nilfs2/segment.c~nilfs2-fix-potential-kernel-bug-due-to-lack-of-writeback-flag-waiting
+++ a/fs/nilfs2/segment.c
@@ -1652,6 +1652,7 @@ static void nilfs_segctor_prepare_write(
if (bh->b_folio != bd_folio) {
if (bd_folio) {
folio_lock(bd_folio);
+ folio_wait_writeback(bd_folio);
folio_clear_dirty_for_io(bd_folio);
folio_start_writeback(bd_folio);
folio_unlock(bd_folio);
@@ -1665,6 +1666,7 @@ static void nilfs_segctor_prepare_write(
if (bh == segbuf->sb_super_root) {
if (bh->b_folio != bd_folio) {
folio_lock(bd_folio);
+ folio_wait_writeback(bd_folio);
folio_clear_dirty_for_io(bd_folio);
folio_start_writeback(bd_folio);
folio_unlock(bd_folio);
@@ -1681,6 +1683,7 @@ static void nilfs_segctor_prepare_write(
}
if (bd_folio) {
folio_lock(bd_folio);
+ folio_wait_writeback(bd_folio);
folio_clear_dirty_for_io(bd_folio);
folio_start_writeback(bd_folio);
folio_unlock(bd_folio);
_
Patches currently in -mm which might be from konishi.ryusuke@xxxxxxxxx are
nilfs2-fix-potential-kernel-bug-due-to-lack-of-writeback-flag-waiting.patch
