On 3/25/19 11:42 AM, Jan Kara wrote:
Hi!
On Sat 23-03-19 15:14:05, Steve Magnani wrote:
...
In contrast, udf_setup_indirect_aext(), which constructs an AED,
has this sequence:
bh = udf_tgetblk(...); // calls sb_getblk()
lock_buffer(bh);
memset(bh->b_data, 0, inode->i_sb->s_blocksize);
set_buffer_uptodate(bh);
unlock_buffer(bh);
mark_buffer_dirty_inode(bh);
// <snip>other code to populate AED data in the block</snip>
In this case the population of the block occurs without
the protection of the lock.
Because the block has been marked dirty, does this mean that
writeback could occur at any point during population?
Yes. Thanks for noticing this!
There is one path through udf_setup_indirect_aext() where
mark_buffer_dirty_inode() gets called again after population is
complete, which I suppose could heal a partial writeout, but there is
also another path in which the buffer does not get marked dirty again.
Generally, we add new extents to the created indirect extent which dirties
the buffer and that should fix the problem. But you are definitely right
that the code is suspicious and should be fixed. Will you send a patch?
Honza
Sure. There's at least one other place where it looked like there might
be a similar issue.
Steve
