Dmitry Monakhov <dmonakhov@xxxxxxxxxx> writes:
> 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
Hm...
Actually there are many places where we submit BHs w/o checks
nojournal code is full of such places.
It looks like we need some sort of AOP_TRUNCATE_PAGE error code
for generic buffer submission path
diff --git a/fs/buffer.c b/fs/buffer.c
index e1632ab..1cf94ec 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3127,6 +3127,10 @@ int __sync_dirty_buffer(struct buffer_head *bh, int rw)
WARN_ON(atomic_read(&bh->b_count) < 1);
lock_buffer(bh);
+ if(unlikely(!buffer_mapped(bh))) {
+ unlock_buffer(bh);
+ return AOP_TRUNCATE_PAGE; /* or EIO */
+ }
if (test_clear_buffer_dirty(bh)) {
get_bh(bh);
bh->b_end_io = end_buffer_write_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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