Messages in this thread Patch in this message | | | Subject | Re: 2.6.33.5 rt23: machine lockup (nfs/autofs related?) | From | john stultz <> | Date | Fri, 09 Jul 2010 12:54:14 -0700 |
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On Fri, 2010-07-09 at 12:02 -0700, Fernando Lopez-Lezcano wrote: > Ok, I got one! (had to go buy a null modem cable, I thought I had one > but it has disappeared since the last time I did this :-)
Great! Sorry to make you go shopping! But this points out the problem nicely.
> Find it below... it keeps spewing stuff every once in a while. Hopefully > this will be enough. No response from the network or the keyboard or > mouse at this point, reset is the only way out. > > I can retest if somebody comes up with a patch... > Thanks. > -- Fernando > > localhost login: ------------[ cut here ]------------ > kernel BUG at kernel/rtmutex.c:808!
So that's a double lock deadlock.
> Call Trace: > [<facf45e6>] ? nfs_refresh_inode_locked+0x79c/0xa1e [nfs] > [<c0465523>] ? rt_spin_lock_fastlock.clone.1+0x26/0x5f > [<c07936b6>] ? rt_spin_unlock+0x8/0xa > [<c0465559>] ? rt_spin_lock_fastlock.clone.1+0x5c/0x5f > [<c07936a2>] ? rt_spin_lock+0x8/0xa > [<c04e08d3>] ? d_materialise_unique+0xa9/0x29e > [<facf55bc>] ? nfs_fhget+0x492/0x51d [nfs] > [<c07936b6>] ? rt_spin_unlock+0x8/0xa > [<facf15a0>] ? nfs_do_filldir+0x27b/0x3a9 [nfs] > [<c04dda9c>] ? filldir64+0x0/0xcb
Looking at d_materialise_unique, I see:
/* Is this an anonymous mountpoint that we could splice * into our tree? */ if (IS_ROOT(alias)) { spin_lock(&alias->d_lock); __d_materialise_dentry(dentry, alias); __d_drop(alias); goto found; }
The problem being that __d_materialise_dentry then tries to lock alias->d_lock and we hang.
Not sure if the following is the right fix but it should avoid the deadlock. Mind testing it to verify things work ok?
Nick: Any race possibility if something catches us between __d_materialise_dentry and d_drop? Or should this be ok?
Signed-off-by: John Stultz <johnstul@us.ibm.com>
diff --git a/fs/dcache.c b/fs/dcache.c index c9d21ae..d37f6f4 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -2159,8 +2159,8 @@ struct dentry *d_materialise_unique(struct dentry *dentry, struct inode *inode) /* Is this an anonymous mountpoint that we could splice * into our tree? */ if (IS_ROOT(alias)) { - spin_lock(&alias->d_lock); __d_materialise_dentry(dentry, alias); + spin_lock(&alias->d_lock); __d_drop(alias); goto found; }
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