FAILED: patch "[PATCH] nilfs2: fix potential bug in end_buffer_async_write" failed to apply to 5.4-stable tree

The patch below does not apply to the 5.4-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-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x 5bc09b397cbf1221f8a8aacb1152650c9195b02b
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024021948-sacrifice-superior-85e5@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..

Possible dependencies:

5bc09b397cbf ("nilfs2: fix potential bug in end_buffer_async_write") ff5710c3f3c2 ("nilfs2: convert nilfs_segctor_prepare_write to use folios") 3cd36212bf75 ("nilfs2: convert nilfs_segctor_complete_write to use folios") 50196f0081ca ("nilfs2: convert nilfs_abort_logs to use folios") 8f46eaf6fd84 ("nilfs2: add nilfs_end_folio_io()")
679bd7ebdd31 ("nilfs2: fix buffer corruption due to concurrent device reads")

thanks,

greg k-h

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

From 5bc09b397cbf1221f8a8aacb1152650c9195b02b Mon Sep 17 00:00:00 2001
From: Ryusuke Konishi <[email protected]>
Date: Sun, 4 Feb 2024 01:16:45 +0900
Subject: [PATCH] nilfs2: fix potential bug in end_buffer_async_write

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.

index 2590a0860eab..2bfb08052d39 100644
@@ -1703,7 +1703,6 @@ static void nilfs_segctor_prepare_write(struct nilfs_sc_info *sci)
 
 		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(struct nilfs_sc_info *sci)
 				}
 				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_head *logs, int err)
 
 		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_head *logs, int err)
 				}
 				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(struct nilfs_sc_info *sci)
 				 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(struct nilfs_sc_info *sci)
 				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;