From: Dan Williams <dan.j.williams@intel.com>

Date: Fri, 18 Sep 2020 12:51:15 -0700

Subject: dm/dax: Fix table reference counts

Patch-mainline: v5.9-rc6

Git-commit: 02186d8897d49b0afd3c80b6cf23437d91024065

References: bsc#1178246

A recent fix to the dm_dax_supported() flow uncovered a latent bug. When

dm_get_live_table() fails it is still required to drop the

srcu_read_lock(). Without this change the lvm2 test-suite triggers this

warning:

    # lvm2-testsuite --only pvmove-abort-all.sh

    WARNING: lock held when returning to user space!

    5.9.0-rc5+ #251 Tainted: G           OE

    ------------------------------------------------

    lvm/1318 is leaving the kernel with locks still held!

    1 lock held by lvm/1318:

     #0: ffff9372abb5a340 (&md->io_barrier){....}-{0:0}, at: dm_get_live_table+0x5/0xb0 [dm_mod]

...and later on this hang signature:

    INFO: task lvm:1344 blocked for more than 122 seconds.

          Tainted: G           OE     5.9.0-rc5+ #251

    "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.

    task:lvm             state:D stack:    0 pid: 1344 ppid:     1 flags:0x00004000

    Call Trace:

     __schedule+0x45f/0xa80

     ? finish_task_switch+0x249/0x2c0

     ? wait_for_completion+0x86/0x110

     schedule+0x5f/0xd0

     schedule_timeout+0x212/0x2a0

     ? __schedule+0x467/0xa80

     ? wait_for_completion+0x86/0x110

     wait_for_completion+0xb0/0x110

     __synchronize_srcu+0xd1/0x160

     ? __bpf_trace_rcu_utilization+0x10/0x10

     __dm_suspend+0x6d/0x210 [dm_mod]

     dm_suspend+0xf6/0x140 [dm_mod]

Fixes: 7bf7eac8d648 ("dax: Arrange for dax_supported check to span multiple devices")

Cc: <stable@vger.kernel.org>

Cc: Jan Kara <jack@suse.cz>

Cc: Alasdair Kergon <agk@redhat.com>

Cc: Mike Snitzer <snitzer@redhat.com>

Reported-by: Adrian Huang <ahuang12@lenovo.com>

Reviewed-by: Ira Weiny <ira.weiny@intel.com>

Tested-by: Adrian Huang <ahuang12@lenovo.com>

Link: https://lore.kernel.org/r/160045867590.25663.7548541079217827340.stgit@dwillia2-desk3.amr.corp.intel.com

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

Acked-by: Michal Kubecek <mkubecek@suse.cz>

---

 drivers/md/dm.c | 5 +++--

 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/md/dm.c

+++ b/drivers/md/dm.c

@@ -1130,15 +1130,16 @@ static bool dm_dax_supported(struct dax_device *dax_dev, struct block_device *bd

 {

 	struct mapped_device *md = dax_get_private(dax_dev);

 	struct dm_table *map;

+	bool ret = false;

 	int srcu_idx;

-	bool ret;

 	map = dm_get_live_table(md, &srcu_idx);

 	if (!map)

-		return false;

+		goto out;

 	ret = dm_table_supports_dax(map, device_supports_dax, &blocksize);

+out:

 	dm_put_live_table(md, srcu_idx);

 	return ret;