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 <h...@suse.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);
}
