[PATCH v1 1/1] aoe: avoid potential deadlock at set_capacity

[Maksim Kiselev <bigunclemax@xxxxxxxxx>]

Move set_capacity() outside of the section procected by (&d->lock).
To avoid possible interrupt unsafe locking scenario:

        CPU0                    CPU1
        ----                    ----
[1] lock(&bdev->bd_size_lock);
                                local_irq_disable();
                            [2] lock(&d->lock);
                            [3] lock(&bdev->bd_size_lock);
   <Interrupt>
[4]  lock(&d->lock);

  *** DEADLOCK ***

Where [1](&bdev->bd_size_lock) hold by zram_add()->set_capacity().
[2]lock(&d->lock) hold by aoeblk_gdalloc(). And aoeblk_gdalloc()
is trying to acquire [3](&bdev->bd_size_lock) at set_capacity() call.
In this situation an attempt to acquire [4]lock(&d->lock) from
aoecmd_cfg_rsp() will lead to deadlock.

So the simplest solution is breaking lock dependency
[2](&d->lock) -> [3](&bdev->bd_size_lock) by moving set_capacity()
outside.

Signed-off-by: Maksim Kiselev <bigunclemax@xxxxxxxxx>
---
 drivers/block/aoe/aoeblk.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
index d2dbf8aaccb5..b1b47d88f5db 100644
--- a/drivers/block/aoe/aoeblk.c
+++ b/drivers/block/aoe/aoeblk.c
@@ -333,6 +333,7 @@ aoeblk_gdalloc(void *vp)
 	struct gendisk *gd;
 	mempool_t *mp;
 	struct blk_mq_tag_set *set;
+	sector_t ssize;
 	ulong flags;
 	int late = 0;
 	int err;
@@ -396,7 +397,7 @@ aoeblk_gdalloc(void *vp)
 	gd->minors = AOE_PARTITIONS;
 	gd->fops = &aoe_bdops;
 	gd->private_data = d;
-	set_capacity(gd, d->ssize);
+	ssize = d->ssize;
 	snprintf(gd->disk_name, sizeof gd->disk_name, "etherd/e%ld.%d",
 		d->aoemajor, d->aoeminor);
 
@@ -405,6 +406,8 @@ aoeblk_gdalloc(void *vp)
 
 	spin_unlock_irqrestore(&d->lock, flags);
 
+	set_capacity(gd, ssize);
+
 	err = device_add_disk(NULL, gd, aoe_attr_groups);
 	if (err)
 		goto out_disk_cleanup;
-- 
2.40.1