BUG at fs/btrfs/locking.c:265

BUG at fs/btrfs/locking.c:265

[Slava Barinov]

Hello,

  Twice for past two days I caught an error with btrfs, you can see a
fragment of dmesg on http://paste.org.ru/?kz4x31 and
http://paste.org.ru/?lwdeu3

  It's a buildserver with jenkins that several times an hour starts a
test script. The only problem I could suppose is using "subvolume
snapshot" feature in script. So, I have about two dozen of snapshots
that refresh periodically.

  Also, I'd like to add small feature request: it'll be good for
mount.btrfs  to show more valuable error messages. For example, if you
try to mount btrfs volume with wrong default subvolume-id, mount.btrfs
says:

 > mount: mount(2) failed: No such file or directory

  And there's nothing in dmesg that could help user to understand what
happened. I've lost about ten minutes trying to understand what does
it want from me.

Best regards,
Slava Barinov.

Re: BUG at fs/btrfs/locking.c:265

[Liu Bo]

On Thu, Dec 27, 2012 at 08:27:11AM +0400, Slava Barinov wrote:
> Hello,
> 
>   Twice for past two days I caught an error with btrfs, you can see a
> fragment of dmesg on http://paste.org.ru/?kz4x31 and
> http://paste.org.ru/?lwdeu3
> 
>   It's a buildserver with jenkins that several times an hour starts a
> test script. The only problem I could suppose is using "subvolume
> snapshot" feature in script. So, I have about two dozen of snapshots
> that refresh periodically.
> 
>   Also, I'd like to add small feature request: it'll be good for
> mount.btrfs  to show more valuable error messages. For example, if you
> try to mount btrfs volume with wrong default subvolume-id, mount.btrfs
> says:
> 
>  > mount: mount(2) failed: No such file or directory
> 
>   And there's nothing in dmesg that could help user to understand what
> happened. I've lost about ten minutes trying to understand what does
> it want from me.

Hi Slava,

Could you please show me what line does 'walk_down_proc+0x2b0/0x2e0 [btrfs]'
refer to?

thanks,
liubo

Re: BUG at fs/btrfs/locking.c:265

[David Sterba]

On Thu, Dec 27, 2012 at 04:07:31PM +0800, Liu Bo wrote:
> On Thu, Dec 27, 2012 at 08:27:11AM +0400, Slava Barinov wrote:
> >   And there's nothing in dmesg that could help user to understand what
> > happened. I've lost about ten minutes trying to understand what does
> > it want from me.
>Could you please show me what line does 'walk_down_proc+0x2b0/0x2e0 [btrfs]'
> refer to?

It's

6578         if (path->locks[level] && level > 0) {
6579                 btrfs_tree_unlock_rw(eb, path->locks[level]);
^^^^
6580                 path->locks[level] = 0;
6581         }
6582         return 0;

which calls btrfs_tree_unlock() and hits the

241 void btrfs_tree_unlock(struct extent_buffer *eb)
242 {
243         int blockers = atomic_read(&eb->blocking_writers);
244
245         BUG_ON(blockers > 1);
246
247         btrfs_assert_tree_locked(eb);

->

263 void btrfs_assert_tree_locked(struct extent_buffer *eb)
264 {
265         BUG_ON(!atomic_read(&eb->write_locks));
266 }


david

Re: BUG at fs/btrfs/locking.c:265

[Liu Bo]

Hi Slava, David,

I've sent a patch to fix the bug(Cced you), could you please check if it
works? :)

thanks,
liubo


On Thu, Dec 27, 2012 at 02:24:37PM +0100, David Sterba wrote:
> On Thu, Dec 27, 2012 at 04:07:31PM +0800, Liu Bo wrote:
> > On Thu, Dec 27, 2012 at 08:27:11AM +0400, Slava Barinov wrote:
> > >   And there's nothing in dmesg that could help user to understand what
> > > happened. I've lost about ten minutes trying to understand what does
> > > it want from me.
> >Could you please show me what line does 'walk_down_proc+0x2b0/0x2e0 [btrfs]'
> > refer to?
> 
> It's
> 
> 6578         if (path->locks[level] && level > 0) {
> 6579                 btrfs_tree_unlock_rw(eb, path->locks[level]);
> ^^^^
> 6580                 path->locks[level] = 0;
> 6581         }
> 6582         return 0;
> 
> which calls btrfs_tree_unlock() and hits the
> 
> 241 void btrfs_tree_unlock(struct extent_buffer *eb)
> 242 {
> 243         int blockers = atomic_read(&eb->blocking_writers);
> 244
> 245         BUG_ON(blockers > 1);
> 246
> 247         btrfs_assert_tree_locked(eb);
> 
> ->
> 
> 263 void btrfs_assert_tree_locked(struct extent_buffer *eb)
> 264 {
> 265         BUG_ON(!atomic_read(&eb->write_locks));
> 266 }
> 
> 
> david