Subject: Re: BUG: sleeping function called from invalid context at kernel/rwsem.c:131 XFS? (was: Re: linux-next: Tree for October 17)

From: Dave Chinner <[email-masked]>
Date: Wed, 22 Oct 2008 19:25:50 +1100

On Wed, Oct 22, 2008 at 06:58:38PM +1100, Dave Chinner wrote:
> On Tue, Oct 21, 2008 at 03:42:16PM +0400, Alexander Beregalov wrote:
> > Bisected to:
> > dd509097cb0b76d3836385f80d6b2d6fd3b97757 is first bad commit
> > commit dd509097cb0b76d3836385f80d6b2d6fd3b97757
> > Author: Lachlan McIlroy <[email-masked]>
> > Date:   Mon Sep 29 14:56:40 2008 +1000
> > 
> >     [XFS] Unlock inode before calling xfs_idestroy()
> > 
> >     Lock debugging reported the ilock was being destroyed without being
> >     unlocked. We don't need to lock the inode until we are going to insert it
> >     into the radix tree.
> 
> Ah, OK, I see the problem, though I don't understand why I'm not
> seeing the might_sleep() triggering all the time given that I always
> build with:
> 
> $ grep SLEEP .config
> CONFIG_DEBUG_SPINLOCK_SLEEP=y
> 
> Basically the above commit moved xfs_ilock() inside
> radix_tree_preload()/radix_tree_preload_end(), which means we are
> taking a rwsem() while we have an elevated preempt count. I'll
> get a patch out to fix it.

Patch below (against the xfs master/linux-next branch) should fix the
regression. I've just started QA on it. Can you please check that
it works for you, Alexander?

Cheers,

Dave.
-- 
Dave Chinner
[email-masked]

XFS: Can't lock inodes in radix tree preload region

When we are inside a radix tree preload region, we cannot
sleep. Recently we moved the inode locking inside the
preload region for the inode radix tree. Fix that,
and fix a missed unlock in another error path in the
same code at the same time.

Signed-off-by: Dave Chinner <[email-masked]>
---
 fs/xfs/xfs_iget.c |   18 +++++++++++-------
 1 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_iget.c b/fs/xfs/xfs_iget.c
index fbc6088..837cae7 100644
--- a/fs/xfs/xfs_iget.c
+++ b/fs/xfs/xfs_iget.c
@@ -159,18 +159,19 @@ xfs_iget_cache_miss(
 		goto out_destroy;
 	}
 
+	if (lock_flags)
+		xfs_ilock(ip, lock_flags);
+
 	/*
 	 * Preload the radix tree so we can insert safely under the
-	 * write spinlock.
+	 * write spinlock. Note that we cannot sleep inside the preload
+	 * region.
 	 */
 	if (radix_tree_preload(GFP_KERNEL)) {
 		error = EAGAIN;
-		goto out_destroy;
+		goto out_unlock;
 	}
 
-	if (lock_flags)
-		xfs_ilock(ip, lock_flags);
-
 	mask = ~(((XFS_INODE_CLUSTER_SIZE(mp) >> mp->m_sb.sb_inodelog)) - 1);
 	first_index = agino & mask;
 	write_lock(&pag->pag_ici_lock);
@@ -181,7 +182,7 @@ xfs_iget_cache_miss(
 		WARN_ON(error != -EEXIST);
 		XFS_STATS_INC(xs_ig_dup);
 		error = EAGAIN;
-		goto out_unlock;
+		goto out_preload_end;
 	}
 
 	/* These values _must_ be set before releasing the radix tree lock! */
@@ -193,9 +194,12 @@ xfs_iget_cache_miss(
 	*ipp = ip;
 	return 0;
 
-out_unlock:
+out_preload_end:
 	write_unlock(&pag->pag_ici_lock);
 	radix_tree_preload_end();
+out_unlock:
+	if (lock_flags)
+		xfs_iunlock(ip, lock_flags);
 out_destroy:
 	xfs_destroy_inode(ip);
 	return error;