Fix deadlock with stacked loop devices (FS#45129).

0001-block-loop-convert-to-per-device-workqueue.patch

@@ -0,0 +1,133 @@
+From ebcacf05168d9791d39c5434164c64b9ef937171 Mon Sep 17 00:00:00 2001
+From: Ming Lei <ming.lei@canonical.com>
+Date: Tue, 5 May 2015 19:49:54 +0800
+Subject: [PATCH 1/2] block: loop: convert to per-device workqueue
+
+Documentation/workqueue.txt:
+	If there is dependency among multiple work items used
+	during memory reclaim, they should be queued to separate
+	wq each with WQ_MEM_RECLAIM.
+
+Loop devices can be stacked, so we have to convert to per-device
+workqueue. One example is Fedora live CD.
+
+Fixes: b5dd2f6047ca108001328aac0e8588edd15f1778
+Cc: stable@vger.kernel.org (v4.0)
+Cc: Justin M. Forbes <jforbes@fedoraproject.org>
+Signed-off-by: Ming Lei <ming.lei@canonical.com>
+Acked-by: Tejun Heo <tj@kernel.org>
+Signed-off-by: Jens Axboe <axboe@fb.com>
+---
+ drivers/block/loop.c | 30 ++++++++++++++----------------
+ drivers/block/loop.h |  1 +
+ 2 files changed, 15 insertions(+), 16 deletions(-)
+
+diff --git a/drivers/block/loop.c b/drivers/block/loop.c
+index d1f168b..fec06d5 100644
+--- a/drivers/block/loop.c
++++ b/drivers/block/loop.c
+@@ -85,8 +85,6 @@ static DEFINE_MUTEX(loop_index_mutex);
+ static int max_part;
+ static int part_shift;
+ 
+-static struct workqueue_struct *loop_wq;
+-
+ /*
+  * Transfer functions
+  */
+@@ -777,6 +775,12 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
+ 	size = get_loop_size(lo, file);
+ 	if ((loff_t)(sector_t)size != size)
+ 		goto out_putf;
++	error = -ENOMEM;
++	lo->wq = alloc_workqueue("kloopd%d",
++			WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0,
++			lo->lo_number);
++	if (!lo->wq)
++		goto out_putf;
+ 
+ 	error = 0;
+ 
+@@ -924,6 +928,8 @@ static int loop_clr_fd(struct loop_device *lo)
+ 	lo->lo_flags = 0;
+ 	if (!part_shift)
+ 		lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
++	destroy_workqueue(lo->wq);
++	lo->wq = NULL;
+ 	mutex_unlock(&lo->lo_ctl_mutex);
+ 	/*
+ 	 * Need not hold lo_ctl_mutex to fput backing file.
+@@ -1477,9 +1483,13 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
+ 		const struct blk_mq_queue_data *bd)
+ {
+ 	struct loop_cmd *cmd = blk_mq_rq_to_pdu(bd->rq);
++	struct loop_device *lo = cmd->rq->q->queuedata;
+ 
+ 	blk_mq_start_request(bd->rq);
+ 
++	if (lo->lo_state != Lo_bound)
++		return -EIO;
++
+ 	if (cmd->rq->cmd_flags & REQ_WRITE) {
+ 		struct loop_device *lo = cmd->rq->q->queuedata;
+ 		bool need_sched = true;
+@@ -1493,9 +1503,9 @@ static int loop_queue_rq(struct blk_mq_hw_ctx *hctx,
+ 		spin_unlock_irq(&lo->lo_lock);
+ 
+ 		if (need_sched)
+-			queue_work(loop_wq, &lo->write_work);
++			queue_work(lo->wq, &lo->write_work);
+ 	} else {
+-		queue_work(loop_wq, &cmd->read_work);
++		queue_work(lo->wq, &cmd->read_work);
+ 	}
+ 
+ 	return BLK_MQ_RQ_QUEUE_OK;
+@@ -1507,9 +1517,6 @@ static void loop_handle_cmd(struct loop_cmd *cmd)
+ 	struct loop_device *lo = cmd->rq->q->queuedata;
+ 	int ret = -EIO;
+ 
+-	if (lo->lo_state != Lo_bound)
+-		goto failed;
+-
+ 	if (write && (lo->lo_flags & LO_FLAGS_READ_ONLY))
+ 		goto failed;
+ 
+@@ -1858,13 +1865,6 @@ static int __init loop_init(void)
+ 		goto misc_out;
+ 	}
+ 
+-	loop_wq = alloc_workqueue("kloopd",
+-			WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);
+-	if (!loop_wq) {
+-		err = -ENOMEM;
+-		goto misc_out;
+-	}
+-
+ 	blk_register_region(MKDEV(LOOP_MAJOR, 0), range,
+ 				  THIS_MODULE, loop_probe, NULL, NULL);
+ 
+@@ -1902,8 +1902,6 @@ static void __exit loop_exit(void)
+ 	blk_unregister_region(MKDEV(LOOP_MAJOR, 0), range);
+ 	unregister_blkdev(LOOP_MAJOR, "loop");
+ 
+-	destroy_workqueue(loop_wq);
+-
+ 	misc_deregister(&loop_misc);
+ }
+ 
+diff --git a/drivers/block/loop.h b/drivers/block/loop.h
+index 301c27f..49564ed 100644
+--- a/drivers/block/loop.h
++++ b/drivers/block/loop.h
+@@ -54,6 +54,7 @@ struct loop_device {
+ 	gfp_t		old_gfp_mask;
+ 
+ 	spinlock_t		lo_lock;
++	struct workqueue_struct *wq;
+ 	struct list_head	write_cmd_head;
+ 	struct work_struct	write_work;
+ 	bool			write_started;
+-- 
+2.4.5
+

0002-block-loop-avoiding-too-many-pending-per-work-I-O.patch

@@ -0,0 +1,52 @@
+From 02a6b08b2706501fb0fe6ff2df2f7d8377f2f69b Mon Sep 17 00:00:00 2001
+From: Ming Lei <ming.lei@canonical.com>
+Date: Tue, 5 May 2015 19:49:55 +0800
+Subject: [PATCH 2/2] block: loop: avoiding too many pending per work I/O
+
+If there are too many pending per work I/O, too many
+high priority work thread can be generated so that
+system performance can be effected.
+
+This patch limits the max_active parameter of workqueue as 16.
+
+This patch fixes Fedora 22 live booting performance
+regression when it is booted from squashfs over dm
+based on loop, and looks the following reasons are
+related with the problem:
+
+- not like other filesyststems(such as ext4), squashfs
+is a bit special, and I observed that increasing I/O jobs
+to access file in squashfs only improve I/O performance a
+little, but it can make big difference for ext4
+
+- nested loop: both squashfs.img and ext3fs.img are mounted
+as loop block, and ext3fs.img is inside the squashfs
+
+- during booting, lots of tasks may run concurrently
+
+Fixes: b5dd2f6047ca108001328aac0e8588edd15f1778
+Cc: stable@vger.kernel.org (v4.0)
+Cc: Justin M. Forbes <jforbes@fedoraproject.org>
+Signed-off-by: Ming Lei <ming.lei@canonical.com>
+Acked-by: Tejun Heo <tj@kernel.org>
+Signed-off-by: Jens Axboe <axboe@fb.com>
+---
+ drivers/block/loop.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/drivers/block/loop.c b/drivers/block/loop.c
+index fec06d5..daaaf70 100644
+--- a/drivers/block/loop.c
++++ b/drivers/block/loop.c
+@@ -777,7 +777,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
+ 		goto out_putf;
+ 	error = -ENOMEM;
+ 	lo->wq = alloc_workqueue("kloopd%d",
+-			WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0,
++			WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 16,
+ 			lo->lo_number);
+ 	if (!lo->wq)
+ 		goto out_putf;
+-- 
+2.4.5
+

PKGBUILD

@@ -5,7 +5,7 @@ pkgbase=linux               # Build stock -ARCH kernel
 #pkgbase=linux-custom       # Build kernel with a different name
 _srcname=linux-4.0
 pkgver=4.0.7
-pkgrel=1
+pkgrel=2
 arch=('i686' 'x86_64')
 url="http://www.kernel.org/"
 license=('GPL2')
@@ -19,6 +19,8 @@ source=("https://www.kernel.org/pub/linux/kernel/v4.x/${_srcname}.tar.xz"
         'config' 'config.x86_64'
         # standard config files for mkinitcpio ramdisk
         'linux.preset'
+        '0001-block-loop-convert-to-per-device-workqueue.patch'
+        '0002-block-loop-avoiding-too-many-pending-per-work-I-O.patch'
         'change-default-console-loglevel.patch')
 sha256sums=('0f2f7d44979bc8f71c4fc5d3308c03499c26a824dd311fdf6eef4dee0d7d5991'
             'SKIP'
@@ -27,6 +29,8 @@ sha256sums=('0f2f7d44979bc8f71c4fc5d3308c03499c26a824dd311fdf6eef4dee0d7d5991'
             'e8d639582697f22333a96aa1614bcf5d9bcf2e6683a3d5296f9cfc64843606f1'
             '5dadd75693e512b77f87f5620e470405b943373613eaf4df561037e9296453be'
             'f0d90e756f14533ee67afda280500511a62465b4f76adcc5effa95a40045179c'
+            '0682df710e8d23f0d420b3b01fbfe409b3911940b1a379b78d9f4a5ac8590386'
+            'af42b1456caee0b0db8f3cc770c78083b40159260b99db4930e503ac7824eacc'
             '1256b241cd477b265a3c2d64bdc19ffe3c9bbcee82ea3994c590c2c76e767d99')
 validpgpkeys=(
               'ABAF11C65A2970B130ABE3C479BE3E4300411886' # Linus Torvalds
@@ -44,6 +48,11 @@ prepare() {
   # add latest fixes from stable queue, if needed
   # http://git.kernel.org/?p=linux/kernel/git/stable/stable-queue.git
 
+  # Fix deadlock with stacked loop devices (FS#45129)
+  # http://marc.info/?l=linux-kernel&m=143280649731902&w=2
+  patch -Np1 -i ../0001-block-loop-convert-to-per-device-workqueue.patch
+  patch -Np1 -i ../0002-block-loop-avoiding-too-many-pending-per-work-I-O.patch
+
   # set DEFAULT_CONSOLE_LOGLEVEL to 4 (same value as the 'quiet' kernel param)
   # remove this when a Kconfig knob is made available by upstream
   # (relevant patch sent upstream: https://lkml.org/lkml/2011/7/26/227)