On Tue, Nov 10, 2020 at 04:36:05PM +0900, Damien Le Moal wrote:
commit e1777d099728a76a8f8090f89649aac961e7e530 upstream.
Commit aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") changed zone locking to using the potentially sleeping wait_on_bit_io() function. This is acceptable when memory backing is enabled as the device queue is in that case marked as blocking, but this triggers a scheduling while in atomic context with memory backing disabled.
Fix this by relying solely on the device zone spinlock for zone information protection without temporarily releasing this lock around null_process_cmd() execution in null_zone_write(). This is OK to do since when memory backing is disabled, command processing does not block and the memory backing lock nullb->lock is unused. This solution avoids the overhead of having to mark a zoned null_blk device queue as blocking when memory backing is unused.
This patch also adds comments to the zone locking code to explain the unusual locking scheme.
Fixes: aa1c09cb65e2 ("null_blk: Fix locking in zoned mode") Reported-by: kernel test robot lkp@intel.com Signed-off-by: Damien Le Moal damien.lemoal@wdc.com Reviewed-by: Christoph Hellwig hch@lst.de Cc: stable@vger.kernel.org Signed-off-by: Jens Axboe axboe@kernel.dk
drivers/block/null_blk.h | 1 + drivers/block/null_blk_zoned.c | 31 +++++++++++++++++++++++++------ 2 files changed, 26 insertions(+), 6 deletions(-)
Now queued up, thanks.
greg k-h