Some devices(nbd) can becomes unoperatable via kill_bdev
so its pagecache will be invalidated and all buffers becomes unmapped.
In that situation we will trigger BUGON on submit_bh.
#Testcase
mkdir -p a/mnt
cd a
truncate -s 1G img
mkfs.ext4 -F img
qemu-nbd -c /dev/nbd0 img
mount /dev/nbd0 /mnt
cp -r /bin/ /mnt&
# Disconnect nbd while cp is active
qemu-nbd -d /dev/nbd0
sync
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/ext4/super.c | 24 +++++++++++++++++++++---
1 file changed, 21 insertions(+), 3 deletions(-)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 3ed01ec..617d8b4a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4320,7 +4320,7 @@ static int ext4_commit_super(struct super_block *sb, int sync)
struct buffer_head *sbh = EXT4_SB(sb)->s_sbh;
int error = 0;
- if (!sbh || block_device_ejected(sb))
+ if (!sbh || !buffer_mapped(sbh) || block_device_ejected(sb))
return error;
if (buffer_write_io_error(sbh)) {
/*
@@ -4368,8 +4368,26 @@ static int ext4_commit_super(struct super_block *sb, int sync)
ext4_superblock_csum_set(sb);
mark_buffer_dirty(sbh);
if (sync) {
- error = __sync_dirty_buffer(sbh,
- test_opt(sb, BARRIER) ? WRITE_FUA : WRITE_SYNC);
+ lock_buffer(sbh);
+ /* superblock bh may be invalidated due to drive failure */
+ if (!buffer_mapped(sbh)) {
+ unlock_buffer(sbh);
+ ext4_msg(sb, KERN_ERR, "Can not write superblock "
+ "because disk cache was invalidated");
+ return -EIO;
+ }
+ if (test_clear_buffer_dirty(sbh)) {
+ get_bh(sbh);
+ sbh->b_end_io = end_buffer_write_sync;
+ error = submit_bh(test_opt(sb, BARRIER) ?
+ WRITE_FUA : WRITE_SYNC, sbh);
+ wait_on_buffer(sbh);
+ if (!error && !buffer_uptodate(sbh))
+ error = -EIO;
+ } else {
+ unlock_buffer(sbh);
+ }
+
if (error)
return error;
--
1.8.3.1
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