linux-kernel - Re: 3.14.23-rt20 - fs,btrfs: fix rt deadlock on extent

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Message-ID: <1424256477.3819.13.camel@gmail.com>
Date:	Wed, 18 Feb 2015 11:47:57 +0100
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	John Kacur <jkacur@...hat.com>,
	Clark Williams <williams@...hat.com>
Subject: Re: 3.14.23-rt20 - fs,btrfs: fix rt deadlock on extent_buffer->lock

On Tue, 2015-02-17 at 12:56 +0100, Sebastian Andrzej Siewior wrote:
> * Mike Galbraith | 2014-11-02 08:31:18 [+0100]:
> 
> >--- a/fs/btrfs/ctree.c
> >+++ b/fs/btrfs/ctree.c
> >@@ -80,7 +80,7 @@ noinline void btrfs_clear_path_blocking(
> > {
> > 	int i;
> > 
> >-#ifdef CONFIG_DEBUG_LOCK_ALLOC
> >+#if (defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_PREEMPT_RT_BASE))
> > 	/* lockdep really cares that we take all of these spinlocks
> > 	 * in the right order.  If any of the locks in the path are not
> > 	 * currently blocking, it is going to complain.  So, make really
> 
> This is gone since commit f82c458 ("btrfs: fix lockups from
> btrfs_clear_path_blocking")

Goody, BTRFS took a modest workout without a whimper.  When that patch
was born, you didn't have to try, deadlock was immediate gratification.

> >@@ -107,7 +107,7 @@ noinline void btrfs_clear_path_blocking(
> > 		}
> > 	}
> > 
> >-#ifdef CONFIG_DEBUG_LOCK_ALLOC
> >+#if (defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_PREEMPT_RT_BASE))
> > 	if (held)
> > 		btrfs_clear_lock_blocking_rw(held, held_rw);
> > #endif
> >--- a/fs/btrfs/extent-tree.c
> >+++ b/fs/btrfs/extent-tree.c
> >@@ -6938,14 +6938,6 @@ use_block_rsv(struct btrfs_trans_handle
> > 		goto again;
> > 	}
> > 
> >-	if (btrfs_test_opt(root, ENOSPC_DEBUG)) {
> >-		static DEFINE_RATELIMIT_STATE(_rs,
> >-				DEFAULT_RATELIMIT_INTERVAL * 10,
> >-				/*DEFAULT_RATELIMIT_BURST*/ 1);
> >-		if (__ratelimit(&_rs))
> >-			WARN(1, KERN_DEBUG
> >-				"BTRFS: block rsv returned %d\n", ret);
> >-	}
> > try_reserve:
> > 	ret = reserve_metadata_bytes(root, block_rsv, blocksize,
> > 				     BTRFS_RESERVE_NO_FLUSH);
> >
> and this look like just a warning with enabled debug that is supressed.
> May I drop this patch?

Yup, that was a cosmetic thing, also suggested by Chris Mason.  BTRFS
seems to now just work.  Hopefully it'll keep on just working, I don't
want to ever go back there :)

	-Mike

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