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    Subject[PATCH 5.8 113/118] dm/dax: Fix table reference counts
    Date
    From: Dan Williams <dan.j.williams@intel.com>

    commit 02186d8897d49b0afd3c80b6cf23437d91024065 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/dm.c | 5 +++--
    1 file changed, 3 insertions(+), 2 deletions(-)

    --- a/drivers/md/dm.c
    +++ b/drivers/md/dm.c
    @@ -1136,15 +1136,16 @@ static bool dm_dax_supported(struct dax_
    {
    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;

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