| Message ID | 20250108092520.1325324-6-hch@lst.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [01/10] block: fix docs for freezing of queue limits updates | expand |
On 1/8/25 6:25 PM, Christoph Hellwig wrote: > queue_attr_store() always freezes a device queue before calling the > attribute store operation. For attributes that control queue limits, the > store operation will also lock the queue limits with a call to > queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may > need to issue commands to a device to obtain limit values from the > hardware with the queue limits locked. This creates a potential ABBA > deadlock situation if a user attempts to modify a limit (thus freezing > the device queue) while the device driver starts a revalidation of the > device queue limits. > > Avoid such deadlock by not freezing the queue before calling the > ->store_limit() method in struct queue_sysfs_entry and instead use the > queue_limits_commit_update_frozen helper to freeze the queue after taking > the limits lock. > > (commit log adapted from a similar patch from Damien Le Moal) > > Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store") > Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store") > Signed-off-by: Christoph Hellwig <hch@lst.de> > Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
On Wed, Jan 08, 2025 at 10:25:02AM +0100, Christoph Hellwig wrote: > queue_attr_store() always freezes a device queue before calling the > attribute store operation. For attributes that control queue limits, the > store operation will also lock the queue limits with a call to > queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may > need to issue commands to a device to obtain limit values from the > hardware with the queue limits locked. This creates a potential ABBA > deadlock situation if a user attempts to modify a limit (thus freezing > the device queue) while the device driver starts a revalidation of the > device queue limits. > > Avoid such deadlock by not freezing the queue before calling the > ->store_limit() method in struct queue_sysfs_entry and instead use the > queue_limits_commit_update_frozen helper to freeze the queue after taking > the limits lock. > > (commit log adapted from a similar patch from Damien Le Moal) > > Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store") > Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store") > Signed-off-by: Christoph Hellwig <hch@lst.de> > Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> > --- > block/blk-sysfs.c | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c > index f36356cbde0b..2de405cb5f10 100644 > --- a/block/blk-sysfs.c > +++ b/block/blk-sysfs.c > @@ -691,22 +691,24 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr, > if (entry->load_module) > entry->load_module(disk, page, length); > > - mutex_lock(&q->sysfs_lock); > - blk_mq_freeze_queue(q); > if (entry->store_limit) { > struct queue_limits lim = queue_limits_start_update(q); > > res = entry->store_limit(disk, page, length, &lim); Looks fine, but now ->store_limit() is called without holding ->sysfs_lock, maybe it should be documented. Reviewed-by: Ming Lei <ming.lei@redhat.com> thanks, Ming
On Wed, Jan 08, 2025 at 06:38:15PM +0800, Ming Lei wrote: > Looks fine, but now ->store_limit() is called without holding > ->sysfs_lock, maybe it should be documented. Ok, I had this in my own commit log, but it got lost when I stole Damien's much better one instead :) I assume you're fine with just documenting it in the commit log?
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index f36356cbde0b..2de405cb5f10 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -691,22 +691,24 @@ queue_attr_store(struct kobject *kobj, struct attribute *attr, if (entry->load_module) entry->load_module(disk, page, length); - mutex_lock(&q->sysfs_lock); - blk_mq_freeze_queue(q); if (entry->store_limit) { struct queue_limits lim = queue_limits_start_update(q); res = entry->store_limit(disk, page, length, &lim); if (res < 0) { queue_limits_cancel_update(q); - } else { - res = queue_limits_commit_update(q, &lim); - if (!res) - res = length; + return res; } - } else { - res = entry->store(disk, page, length); + + res = queue_limits_commit_update_frozen(q, &lim); + if (res) + return res; + return length; } + + mutex_lock(&q->sysfs_lock); + blk_mq_freeze_queue(q); + res = entry->store(disk, page, length); blk_mq_unfreeze_queue(q); mutex_unlock(&q->sysfs_lock); return res;
queue_attr_store() always freezes a device queue before calling the attribute store operation. For attributes that control queue limits, the store operation will also lock the queue limits with a call to queue_limits_start_update(). However, some drivers (e.g. SCSI sd) may need to issue commands to a device to obtain limit values from the hardware with the queue limits locked. This creates a potential ABBA deadlock situation if a user attempts to modify a limit (thus freezing the device queue) while the device driver starts a revalidation of the device queue limits. Avoid such deadlock by not freezing the queue before calling the ->store_limit() method in struct queue_sysfs_entry and instead use the queue_limits_commit_update_frozen helper to freeze the queue after taking the limits lock. (commit log adapted from a similar patch from Damien Le Moal) Fixes: ff956a3be95b ("block: use queue_limits_commit_update in queue_discard_max_store") Fixes: 0327ca9d53bf ("block: use queue_limits_commit_update in queue_max_sectors_store") Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Nilay Shroff <nilay@linux.ibm.com> --- block/blk-sysfs.c | 18 ++++++++++-------- 1 file changed, 10 insertions(+), 8 deletions(-)