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From: Christoph Hellwig <hch@lst.de>
To: Jens Axboe <axboe@kernel.dk>
Cc: Hillf Danton <hdanton@sina.com>,
	Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	"Reviewed-by : Tyler Hicks" <tyhicks@linux.microsoft.com>,
	linux-block@vger.kernel.org
Subject: [PATCH 7/8] loop: move loop device deletion out of loop_ctl_mutex
Date: Thu, 26 Aug 2021 15:38:09 +0200	[thread overview]
Message-ID: <20210826133810.3700-8-hch@lst.de> (raw)
In-Reply-To: <20210826133810.3700-1-hch@lst.de>

To avoid complex lock ordering issues always delete loop devices outside
of loop_ctl_mutex.  In loop_control_remove the Lo_deleting state can
be used to prevent further lookups, and given that module unload is
synchronized vs new opens of the control device and thus ioctls there
is no need for locks there at all.

Based on patches from Hillf Danton <hdanton@sina.com> and
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>.

Reported-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/loop.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 6ee4b046bdcc..cb857d5e8313 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2478,7 +2478,11 @@ static int loop_control_remove(int idx)
 	mutex_unlock(&lo->lo_mutex);
 
 	idr_remove(&loop_index_idr, lo->lo_number);
+	mutex_unlock(&loop_ctl_mutex);
+
 	loop_remove(lo);
+	return 0;
+
 out_unlock_ctrl:
 	mutex_unlock(&loop_ctl_mutex);
 	return ret;
@@ -2609,11 +2613,12 @@ static void __exit loop_exit(void)
 	unregister_blkdev(LOOP_MAJOR, "loop");
 	misc_deregister(&loop_misc);
 
-	mutex_lock(&loop_ctl_mutex);
+	/*
+	 * No need for loop_ctl_mutex given that no new ioctls and thus
+	 * additions and removals can happen in parallel to module unloading.
+	 */
 	idr_for_each_entry(&loop_index_idr, lo, id)
 		loop_remove(lo);
-	mutex_unlock(&loop_ctl_mutex);
-
 	idr_destroy(&loop_index_idr);
 }
 
-- 
2.30.2


  parent reply	other threads:[~2021-08-26 13:48 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-26 13:38 sort out the lock order in the loop driver v2 Christoph Hellwig
2021-08-26 13:38 ` [PATCH 1/8] cryptoloop: fix a sparse annotation Christoph Hellwig
2021-08-26 13:38 ` [PATCH 2/8] loop: remove the unused idx argument to loop_control_get_free Christoph Hellwig
2021-08-26 13:38 ` [PATCH 3/8] loop: remove the ->ioctl method in loop_func_table Christoph Hellwig
2021-08-26 13:38 ` [PATCH 4/8] loop: return void from the ->release " Christoph Hellwig
2021-08-26 13:38 ` [PATCH 5/8] loop: merge the cryptoloop module into the main loop module Christoph Hellwig
2021-08-26 16:31   ` Milan Broz
2021-08-26 16:34     ` Christoph Hellwig
2021-08-26 16:44       ` Milan Broz
2021-08-27  6:45         ` Christoph Hellwig
2021-08-27 11:33           ` Tetsuo Handa
2021-08-27 15:38             ` Christoph Hellwig
2021-08-26 13:38 ` [PATCH 6/8] loop: devirtualize transfer transformations Christoph Hellwig
2021-08-26 13:38 ` Christoph Hellwig [this message]
2021-08-26 13:38 ` [PATCH 8/8] loop: avoid holding loop_ctl_mutex over add_disk Christoph Hellwig
2021-08-27  0:30 ` sort out the lock order in the loop driver v2 Tetsuo Handa
2021-08-27  6:40   ` Christoph Hellwig
2021-08-27  7:46     ` Tetsuo Handa
2021-08-27 15:34       ` Christoph Hellwig
     [not found] ` <20210827130259.2622-1-hdanton@sina.com>
2021-08-27 14:10   ` Tetsuo Handa
     [not found]   ` <20210828035114.2762-1-hdanton@sina.com>
2021-08-28  5:17     ` Tetsuo Handa

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