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authorDerek Basehore <dbasehore@chromium.org>2012-12-18 12:27:20 -0800
committerJens Axboe <axboe@kernel.dk>2012-12-19 20:36:10 +0100
commit12c2bdb232168511c8dd54d6626549391a228918 (patch)
tree8b9179df57d7ddd596a57d465cce4e0949795d25 /block/genhd.c
parentaea24a8bbc81c8b404e4e293fb37aefaf388d35d (diff)
downloadkernel-12c2bdb232168511c8dd54d6626549391a228918.tar.gz
block: prevent race/cleanup
Remove a race condition which causes a warning in disk_clear_events. This is a race between disk_clear_events() and disk_flush_events(). ev->clearing will be altered by disk_flush_events() even though we are blocking event checking through disk_flush_events(). If this happens after ev->clearing was cleared for disk_clear_events(), this can cause the WARN_ON_ONCE() in that function to be triggered. This change also has disk_clear_events() not go through a workqueue. Since we have to wait for the work to complete, we should just call the function directly. Also, since this work cannot be put on a freezable workqueue, it will have to contend with increased demand, so calling the function directly avoids this. [akpm@linux-foundation.org: fix spello in comment] Signed-off-by: Derek Basehore <dbasehore@chromium.org> Cc: Mandeep Singh Baines <msb@chromium.org> Cc: Jens Axboe <axboe@kernel.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/genhd.c')
-rw-r--r--block/genhd.c45
1 files changed, 30 insertions, 15 deletions
diff --git a/block/genhd.c b/block/genhd.c
index 33a3b38aa4b2..3993ebf4135f 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -35,6 +35,8 @@ static DEFINE_IDR(ext_devt_idr);
static struct device_type disk_type;
+static void disk_check_events(struct disk_events *ev,
+ unsigned int *clearing_ptr);
static void disk_alloc_events(struct gendisk *disk);
static void disk_add_events(struct gendisk *disk);
static void disk_del_events(struct gendisk *disk);
@@ -1549,6 +1551,7 @@ unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
const struct block_device_operations *bdops = disk->fops;
struct disk_events *ev = disk->ev;
unsigned int pending;
+ unsigned int clearing = mask;
if (!ev) {
/* for drivers still using the old ->media_changed method */
@@ -1558,41 +1561,53 @@ unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
return 0;
}
- /* tell the workfn about the events being cleared */
+ disk_block_events(disk);
+
+ /*
+ * store the union of mask and ev->clearing on the stack so that the
+ * race with disk_flush_events does not cause ambiguity (ev->clearing
+ * can still be modified even if events are blocked).
+ */
spin_lock_irq(&ev->lock);
- ev->clearing |= mask;
+ clearing |= ev->clearing;
+ ev->clearing = 0;
spin_unlock_irq(&ev->lock);
- /* uncondtionally schedule event check and wait for it to finish */
- disk_block_events(disk);
+ disk_check_events(ev, &clearing);
/*
- * We need to put the work on system_nrt_wq here since there is a
- * deadlock that happens while probing a usb device while suspending. If
- * we put work on a freezable workqueue here, a usb probe will wait here
- * until the workqueue is unfrozen during suspend. Since suspend waits
- * on all probes to complete, we have a deadlock
+ * if ev->clearing is not 0, the disk_flush_events got called in the
+ * middle of this function, so we want to run the workfn without delay.
*/
- queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
- flush_delayed_work(&ev->dwork);
- __disk_unblock_events(disk, false);
+ __disk_unblock_events(disk, ev->clearing ? true : false);
/* then, fetch and clear pending events */
spin_lock_irq(&ev->lock);
- WARN_ON_ONCE(ev->clearing & mask); /* cleared by workfn */
pending = ev->pending & mask;
ev->pending &= ~mask;
spin_unlock_irq(&ev->lock);
+ WARN_ON_ONCE(clearing & mask);
return pending;
}
+/*
+ * Separate this part out so that a different pointer for clearing_ptr can be
+ * passed in for disk_clear_events.
+ */
static void disk_events_workfn(struct work_struct *work)
{
struct delayed_work *dwork = to_delayed_work(work);
struct disk_events *ev = container_of(dwork, struct disk_events, dwork);
+
+ disk_check_events(ev, &ev->clearing);
+}
+
+static void disk_check_events(struct disk_events *ev,
+ unsigned int *clearing_ptr)
+{
struct gendisk *disk = ev->disk;
char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
- unsigned int clearing = ev->clearing;
+ unsigned int clearing = *clearing_ptr;
unsigned int events;
unsigned long intv;
int nr_events = 0, i;
@@ -1605,7 +1620,7 @@ static void disk_events_workfn(struct work_struct *work)
events &= ~ev->pending;
ev->pending |= events;
- ev->clearing &= ~clearing;
+ *clearing_ptr &= ~clearing;
intv = disk_events_poll_jiffies(disk);
if (!ev->block && intv)