| Message ID | 20220603021905.1441419-1-damien.lemoal@opensource.wdc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | block: Fix potential deadlock in blk_ia_range_sysfs_show() | expand |
On Fri, 3 Jun 2022 11:19:05 +0900, Damien Le Moal wrote: > When being read, a sysfs attribute is already protected against removal > with the kobject node active reference counter. As a result, in > blk_ia_range_sysfs_show(), there is no need to take the queue sysfs > lock when reading the value of a range attribute. Using the queue sysfs > lock in this function creates a potential deadlock situation with the > disk removal, something that a lockdep signals with a splat when the > device is removed: > > [...] Applied, thanks! [1/1] block: Fix potential deadlock in blk_ia_range_sysfs_show() commit: 41e46b3c2aa24f755b2ae9ec4ce931ba5f0d8532 Best regards,
diff --git a/block/blk-ia-ranges.c b/block/blk-ia-ranges.c index 18c68d8b9138..56ed48d2954e 100644 --- a/block/blk-ia-ranges.c +++ b/block/blk-ia-ranges.c @@ -54,13 +54,8 @@ static ssize_t blk_ia_range_sysfs_show(struct kobject *kobj, container_of(attr, struct blk_ia_range_sysfs_entry, attr); struct blk_independent_access_range *iar = container_of(kobj, struct blk_independent_access_range, kobj); - ssize_t ret; - mutex_lock(&iar->queue->sysfs_lock); - ret = entry->show(iar, buf); - mutex_unlock(&iar->queue->sysfs_lock); - - return ret; + return entry->show(iar, buf); } static const struct sysfs_ops blk_ia_range_sysfs_ops = {
When being read, a sysfs attribute is already protected against removal with the kobject node active reference counter. As a result, in blk_ia_range_sysfs_show(), there is no need to take the queue sysfs lock when reading the value of a range attribute. Using the queue sysfs lock in this function creates a potential deadlock situation with the disk removal, something that a lockdep signals with a splat when the device is removed: [ 760.703551] Possible unsafe locking scenario: [ 760.703551] [ 760.703554] CPU0 CPU1 [ 760.703556] ---- ---- [ 760.703558] lock(&q->sysfs_lock); [ 760.703565] lock(kn->active#385); [ 760.703573] lock(&q->sysfs_lock); [ 760.703579] lock(kn->active#385); [ 760.703587] [ 760.703587] *** DEADLOCK *** Solve this by removing the mutex_lock()/mutex_unlock() calls from blk_ia_range_sysfs_show(). Fixes: a2247f19ee1c ("block: Add independent access ranges support") Cc: stable@vger.kernel.org Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com> --- block/blk-ia-ranges.c | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-)