FAILED: patch "[PATCH] nilfs2: fix potential kernel bug due to lack of writeback" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x a4ca369ca221bb7e06c725792ac107f0e48e82e7
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024061324-prize-qualifier-989e@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

a4ca369ca221 ("nilfs2: fix potential kernel bug due to lack of writeback flag waiting") ff5710c3f3c2 ("nilfs2: convert nilfs_segctor_prepare_write to use folios")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From a4ca369ca221bb7e06c725792ac107f0e48e82e7 Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <[email protected]>
Date: Thu, 30 May 2024 23:15:56 +0900
Subject: [PATCH] nilfs2: fix potential kernel bug due to lack of writeback
flag waiting

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.

index 60d4f59f7665..6ea81f1d5094 100644
@@ -1652,6 +1652,7 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
 			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(struct nilfs_sc_info *sci)
 			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(struct nilfs_sc_info *sci)
 	}
 	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);