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Date: Wed, 18 Jan 2017 10:48:16 +0100
From: Hannes Reinecke <hare@...e.de>
To: Jens Axboe <axboe@...nel.dk>
Cc: Christoph Hellwig <hch@....de>,
Johannes Thumshirn <jth@...nel.org>,
linux-block@...r.kernel.org,
Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
Hannes Reinecke <hare@...e.de>, Hannes Reinecke <hare@...e.com>
Subject: [PATCH] genhd: Do not hold event lock when scheduling workqueue elements
When scheduling workqueue elements the callback function might be called
directly, so holding the event lock is potentially dangerous as it might
lead to a deadlock:
[ 989.542827] INFO: task systemd-udevd:459 blocked for more than 480 seconds.
[ 989.609721] Not tainted 4.10.0-rc4+ #546
[ 989.648545] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 989.716429] systemd-udevd D13368 459 1 0x00000004
[ 989.716435] Call Trace:
[ 989.716444] __schedule+0x2f2/0xb10
[ 989.716447] schedule+0x3d/0x90
[ 989.716449] schedule_timeout+0x2fc/0x600
[ 989.716451] ? wait_for_completion+0xac/0x110
[ 989.716456] ? mark_held_locks+0x66/0x90
[ 989.716458] ? _raw_spin_unlock_irq+0x2c/0x40
[ 989.716460] ? trace_hardirqs_on_caller+0x111/0x1e0
[ 989.716461] wait_for_completion+0xb4/0x110
[ 989.716464] ? wake_up_q+0x80/0x80
[ 989.716469] flush_work+0x1ea/0x2a0
[ 989.716470] ? flush_work+0x24e/0x2a0
[ 989.716472] ? destroy_worker+0xd0/0xd0
[ 989.716474] __cancel_work_timer+0x11a/0x1e0
[ 989.716476] ? trace_hardirqs_on_caller+0x111/0x1e0
[ 989.716477] cancel_delayed_work_sync+0x13/0x20
[ 989.716482] disk_block_events+0x82/0x90
[ 989.716487] __blkdev_get+0x58/0x450
[ 989.716488] blkdev_get+0x1ce/0x340
[ 989.716490] ? _raw_spin_unlock+0x27/0x40
[ 989.716492] blkdev_open+0x5b/0x70
[ 989.716501] do_dentry_open+0x213/0x310
[ 989.716505] ? blkdev_get_by_dev+0x50/0x50
[ 989.716507] vfs_open+0x4f/0x80
[ 989.716518] ? may_open+0x9b/0x100
[ 989.716521] path_openat+0x48a/0xdc0
[ 989.716527] ? _crng_backtrack_protect+0x30/0x80
[ 989.716530] do_filp_open+0x7e/0xd0
[ 989.716533] ? _raw_spin_unlock+0x27/0x40
[ 989.716537] ? __alloc_fd+0xf7/0x210
[ 989.716539] do_sys_open+0x115/0x1f0
[ 989.716542] SyS_open+0x1e/0x20
[ 989.716546] entry_SYSCALL_64_fastpath+0x23/0xc6
Signed-off-by: Hannes Reinecke <hare@...e.com>
diff --git a/block/genhd.c b/block/genhd.c
index fcd6d4f..ae46caa 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -1426,8 +1426,7 @@ struct disk_events {
struct gendisk *disk; /* the associated disk */
spinlock_t lock;
- struct mutex block_mutex; /* protects blocking */
- int block; /* event blocking depth */
+ atomic_t block; /* event blocking depth */
unsigned int pending; /* events already sent out */
unsigned int clearing; /* events being cleared */
@@ -1488,26 +1487,13 @@ static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
void disk_block_events(struct gendisk *disk)
{
struct disk_events *ev = disk->ev;
- unsigned long flags;
- bool cancel;
if (!ev)
return;
- /*
- * Outer mutex ensures that the first blocker completes canceling
- * the event work before further blockers are allowed to finish.
- */
- mutex_lock(&ev->block_mutex);
-
- spin_lock_irqsave(&ev->lock, flags);
- cancel = !ev->block++;
- spin_unlock_irqrestore(&ev->lock, flags);
-
- if (cancel)
+ if (atomic_inc_return(&ev->block) == 1)
cancel_delayed_work_sync(&disk->ev->dwork);
- mutex_unlock(&ev->block_mutex);
}
static void __disk_unblock_events(struct gendisk *disk, bool check_now)
@@ -1516,23 +1502,18 @@ static void __disk_unblock_events(struct gendisk *disk, bool check_now)
unsigned long intv;
unsigned long flags;
- spin_lock_irqsave(&ev->lock, flags);
-
- if (WARN_ON_ONCE(ev->block <= 0))
- goto out_unlock;
-
- if (--ev->block)
- goto out_unlock;
+ if (atomic_dec_return(&ev->block) > 0)
+ return;
+ spin_lock_irqsave(&ev->lock, flags);
intv = disk_events_poll_jiffies(disk);
+ spin_unlock_irqrestore(&ev->lock, flags);
if (check_now)
queue_delayed_work(system_freezable_power_efficient_wq,
&ev->dwork, 0);
else if (intv)
queue_delayed_work(system_freezable_power_efficient_wq,
&ev->dwork, intv);
-out_unlock:
- spin_unlock_irqrestore(&ev->lock, flags);
}
/**
@@ -1572,10 +1553,10 @@ void disk_flush_events(struct gendisk *disk, unsigned int mask)
spin_lock_irq(&ev->lock);
ev->clearing |= mask;
- if (!ev->block)
+ spin_unlock_irq(&ev->lock);
+ if (!atomic_read(&ev->block))
mod_delayed_work(system_freezable_power_efficient_wq,
&ev->dwork, 0);
- spin_unlock_irq(&ev->lock);
}
/**
@@ -1666,12 +1647,11 @@ static void disk_check_events(struct disk_events *ev,
*clearing_ptr &= ~clearing;
intv = disk_events_poll_jiffies(disk);
- if (!ev->block && intv)
+ spin_unlock_irq(&ev->lock);
+ if (!atomic_read(&ev->block) && intv)
queue_delayed_work(system_freezable_power_efficient_wq,
&ev->dwork, intv);
- spin_unlock_irq(&ev->lock);
-
/*
* Tell userland about new events. Only the events listed in
* @disk->events are reported. Unlisted events are processed the
@@ -1824,8 +1804,7 @@ static void disk_alloc_events(struct gendisk *disk)
INIT_LIST_HEAD(&ev->node);
ev->disk = disk;
spin_lock_init(&ev->lock);
- mutex_init(&ev->block_mutex);
- ev->block = 1;
+ atomic_set(&ev->block, 1);
ev->poll_msecs = -1;
INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);
@@ -1870,6 +1849,6 @@ static void disk_del_events(struct gendisk *disk)
static void disk_release_events(struct gendisk *disk)
{
/* the block count should be 1 from disk_del_events() */
- WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
+ WARN_ON_ONCE(disk->ev && atomic_read(&disk->ev->block) != 1);
kfree(disk->ev);
}
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