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From: NeilBrown <neilb@suse.de>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
	Peter Zijlstra <peterz@infradead.org>, LKP <lkp@01.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Shaohua Li <shli@kernel.org>,
	Dan Williams <dan.j.williams@intel.com>,
	"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: __might_sleep() warnings on v3.19-rc6
Date: Mon, 2 Feb 2015 17:09:37 +1100
Message-ID: <20150202170937.4b5ffcb0@notabene.brown> (raw)
In-Reply-To: <CA+55aFyR-ZK9Y2KkxbcTnMOcCc243ZKD6AKTuktpmyE0HCUcPw@mail.gmail.com>


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On Sun, 1 Feb 2015 21:08:12 -0800 Linus Torvalds
<torvalds@linux-foundation.org> wrote:

> On Sun, Feb 1, 2015 at 3:03 PM, NeilBrown <neilb@suse.de> wrote:
> >
> > I guess I could
> >       __set_current_state(TASK_RUNNING);
> > somewhere to defeat the warning, and add a comment explaining why.
> >
> > Would that be a good thing?
> 
> Use "sched_annotate_sleep()" instead, but yes, add a comment about why it's ok.
> 
>                         Linus
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OK - following patch is queued to appear in a pull request tomorrow  (I hope).

Thanks,
NeilBrown

From: NeilBrown <neilb@suse.de>
Date: Mon, 2 Feb 2015 17:08:03 +1100
Subject: [PATCH] md/bitmap: fix a might_sleep() warning.

commit 8eb23b9f35aae413140d3fda766a98092c21e9b0
    sched: Debug nested sleeps

causes false-positive warnings in RAID5 code.

This annotation removes them and adds a comment
explaining why there is no real problem.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index da3604e73e8a..1695ee5f3ffc 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -72,6 +72,19 @@ __acquires(bitmap->lock)
 	/* this page has not been allocated yet */
 
 	spin_unlock_irq(&bitmap->lock);
+	/* It is possible that this is being called inside a
+	 * prepare_to_wait/finish_wait loop from raid5c:make_request().
+	 * In general it is not permitted to sleep in that context as it
+	 * can cause the loop to spin freely.
+	 * That doesn't apply here as we can only reach this point
+	 * once with any loop.
+	 * When this function completes, either bp[page].map or
+	 * bp[page].hijacked.  In either case, this function will
+	 * abort before getting to this point again.  So there is
+	 * no risk of a free-spin, and so it is safe to assert
+	 * that sleeping here is allowed.
+	 */
+	sched_annotate_sleep();
 	mappage = kzalloc(PAGE_SIZE, GFP_NOIO);
 	spin_lock_irq(&bitmap->lock);
 

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  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20141028142541.GA19097@wfg-t540p.sh.intel.com>
2015-02-01  3:43 ` Fengguang Wu
2015-02-01 23:03   ` NeilBrown
2015-02-02  4:58     ` NeilBrown
2015-02-02  5:08     ` Linus Torvalds
2015-02-02  6:09       ` NeilBrown [this message]
2015-02-05 16:16   ` Chris Mason

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