| Message ID | 20200414120409.293749-3-jlayton@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | vfs: have syncfs() return error when there are writeback errors | expand |
On Tue 14-04-20 08:04:09, Jeff Layton wrote: > From: Jeff Layton <jlayton@redhat.com> > > When syncing out a block device (a'la __sync_blockdev), any error > encountered will only be recorded in the bd_inode's mapping. When the > blockdev contains a filesystem however, we'd like to also record the > error in the super_block that's stored there. > > Make mark_buffer_write_io_error also record the error in the > corresponding super_block when a writeback error occurs and the block > device contains a mounted superblock. > > Signed-off-by: Jeff Layton <jlayton@kernel.org> The patch looks good to me. I'd just note that bh->b_bdev->bd_super dereference is safe only because we will flush all dirty data when unmounting a filesystem which is somewhat tricky. Maybe that warrants a comment? Otherwise feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza > --- > fs/buffer.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/fs/buffer.c b/fs/buffer.c > index f73276d746bb..a9d986d27fa1 100644 > --- a/fs/buffer.c > +++ b/fs/buffer.c > @@ -1160,6 +1160,8 @@ void mark_buffer_write_io_error(struct buffer_head *bh) > mapping_set_error(bh->b_page->mapping, -EIO); > if (bh->b_assoc_map) > mapping_set_error(bh->b_assoc_map, -EIO); > + if (bh->b_bdev->bd_super) > + errseq_set(&bh->b_bdev->bd_super->s_wb_err, -EIO); > } > EXPORT_SYMBOL(mark_buffer_write_io_error); > > -- > 2.25.2 >
On Tue, 2020-04-14 at 18:26 +0200, Jan Kara wrote: > On Tue 14-04-20 08:04:09, Jeff Layton wrote: > > From: Jeff Layton <jlayton@redhat.com> > > > > When syncing out a block device (a'la __sync_blockdev), any error > > encountered will only be recorded in the bd_inode's mapping. When the > > blockdev contains a filesystem however, we'd like to also record the > > error in the super_block that's stored there. > > > > Make mark_buffer_write_io_error also record the error in the > > corresponding super_block when a writeback error occurs and the block > > device contains a mounted superblock. > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > The patch looks good to me. I'd just note that bh->b_bdev->bd_super > dereference is safe only because we will flush all dirty data when > unmounting a filesystem which is somewhat tricky. Maybe that warrants a > comment? Otherwise feel free to add: > > Reviewed-by: Jan Kara <jack@suse.cz> Oh, hmm...now that I look again, I'm not sure this is actually safe. bh->b_bdev gets cleared out as we discard the buffer, so I don't think that could end up getting zeroed while we're still using it. The bd_super pointer gets zeroed out in kill_block_super, and after that point it calls sync_blockdev(). Could writeback error processing race with kill_block_super such that bd_inode gets set to NULL after we test it but before we dereference it? Thanks,
On Tue 14-04-20 14:37:21, Jeff Layton wrote: > On Tue, 2020-04-14 at 18:26 +0200, Jan Kara wrote: > > On Tue 14-04-20 08:04:09, Jeff Layton wrote: > > > From: Jeff Layton <jlayton@redhat.com> > > > > > > When syncing out a block device (a'la __sync_blockdev), any error > > > encountered will only be recorded in the bd_inode's mapping. When the > > > blockdev contains a filesystem however, we'd like to also record the > > > error in the super_block that's stored there. > > > > > > Make mark_buffer_write_io_error also record the error in the > > > corresponding super_block when a writeback error occurs and the block > > > device contains a mounted superblock. > > > > > > Signed-off-by: Jeff Layton <jlayton@kernel.org> > > > > The patch looks good to me. I'd just note that bh->b_bdev->bd_super > > dereference is safe only because we will flush all dirty data when > > unmounting a filesystem which is somewhat tricky. Maybe that warrants a > > comment? Otherwise feel free to add: > > > > Reviewed-by: Jan Kara <jack@suse.cz> > > Oh, hmm...now that I look again, I'm not sure this is actually safe. > > bh->b_bdev gets cleared out as we discard the buffer, so I don't think > that could end up getting zeroed while we're still using it. Correct. > The bd_super pointer gets zeroed out in kill_block_super, and after that > point it calls sync_blockdev(). Could writeback error processing race > with kill_block_super such that bd_inode gets set to NULL after we test > it but before we dereference it? Yeah, you're right. But you can avoid the race with READ_ONCE(bh->b_bdev->bd_super) and a big fat comment explaining why it is safe... :) Or you could be less daring and put rcu protection there because superblocks are RCU freed... Honza
diff --git a/fs/buffer.c b/fs/buffer.c index f73276d746bb..a9d986d27fa1 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1160,6 +1160,8 @@ void mark_buffer_write_io_error(struct buffer_head *bh) mapping_set_error(bh->b_page->mapping, -EIO); if (bh->b_assoc_map) mapping_set_error(bh->b_assoc_map, -EIO); + if (bh->b_bdev->bd_super) + errseq_set(&bh->b_bdev->bd_super->s_wb_err, -EIO); } EXPORT_SYMBOL(mark_buffer_write_io_error);