Re: [PATCH] Suppress a kernel warning in case the prep function returns BLKPREP_DEFER

Damien Le Moal
2017-10-23T05:49:54Z

On 10/20/17 20:46, Bart Van Assche wrote:
> The legacy block layer handles requests as follows:
> - If the prep function returns BLKPREP_OK, let blk_peek_request()
> return the pointer to that request.
> - If the prep function returns BLKPREP_DEFER, keep the RQF_STARTED
> flag and retry calling the prep function later.
> - If the prep function returns BLKPREP_KILL or BLKPREP_INVALID, end
> the request.
>
> In none of these cases it is correct to clear the SCMD_INITIALIZED
> flag from inside scsi_prep_fn(). Since scsi_prep_fn() already
> guarantees that scsi_init_command() will be called once even if
> scsi_prep_fn() is called multiple times, remove the code that clears
> SCMD_INITIALIZED from scsi_prep_fn().
>
> The scsi-mq code handles requests as follows:
> - If scsi_mq_prep_fn() returns BLKPREP_OK, set the RQF_DONTPREP flag
> and submit the request to the SCSI LLD.
> - If scsi_mq_prep_fn() returns BLKPREP_DEFER, call
> blk_mq_delay_run_hw_queue() and return BLK_STS_RESOURCE.
> - If the prep function returns BLKPREP_KILL or BLKPREP_INVALID, call
> scsi_mq_uninit_cmd() and let the blk-mq core end the request.
>
> In none of these cases scsi_mq_prep_fn() should clear the
> SCMD_INITIALIZED flag. Hence remove the code from scsi_mq_prep_fn()
> function that clears that flag.
>
> This patch avoids that the following warning is triggered when using
> the legacy block layer:
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 4198 at drivers/scsi/scsi_lib.c:654 scsi_end_request+0x1de/0x220
> CPU: 1 PID: 4198 Comm: mkfs.f2fs Not tainted 4.14.0-rc5+ #1
> task: ffff91c147a4b800 task.stack: ffffb282c37b8000
> RIP: 0010:scsi_end_request+0x1de/0x220
> Call Trace:
> <IRQ>
> scsi_io_completion+0x204/0x5e0
> scsi_finish_command+0xce/0xe0
> scsi_softirq_done+0x126/0x130
> blk_done_softirq+0x6e/0x80
> __do_softirq+0xcf/0x2a8
> irq_exit+0xab/0xb0
> do_IRQ+0x7b/0xc0
> common_interrupt+0x90/0x90
> </IRQ>
> RIP: 0010:_raw_spin_unlock_irqrestore+0x9/0x10
> __test_set_page_writeback+0xc7/0x2c0
> __block_write_full_page+0x158/0x3b0
> block_write_full_page+0xc4/0xd0
> blkdev_writepage+0x13/0x20
> __writepage+0x12/0x40
> write_cache_pages+0x204/0x500
> generic_writepages+0x48/0x70
> blkdev_writepages+0x9/0x10
> do_writepages+0x34/0xc0
> __filemap_fdatawrite_range+0x6c/0x90
> file_write_and_wait_range+0x31/0x90
> blkdev_fsync+0x16/0x40
> vfs_fsync_range+0x44/0xa0
> do_fsync+0x38/0x60
> SyS_fsync+0xb/0x10
> entry_SYSCALL_64_fastpath+0x13/0x94
> ---[ end trace 86e8ef85a4a6c1d1 ]---
>
> Fixes: commit 64104f703212 ("scsi: Call scsi_initialize_rq() for filesystem requests")
> Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
> Cc: Damien Le Moal <damien.lemoal@wdc.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Hannes Reinecke <hare@suse.com>
> Cc: Johannes Thumshirn <jthumshirn@suse.de>
> ---
> drivers/scsi/scsi_lib.c | 8 +-------
> 1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 1779c8e91d09..5745af3e81bd 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1378,8 +1378,6 @@ static int scsi_prep_fn(struct request_queue *q, struct request *req)
>
> ret = scsi_setup_cmnd(sdev, req);
> out:
> - if (ret != BLKPREP_OK)
> - cmd->flags &= ~SCMD_INITIALIZED;
> return scsi_prep_return(q, req, ret);
> }
>
> @@ -1899,7 +1897,6 @@ static int scsi_mq_prep_fn(struct request *req)
> struct scsi_device *sdev = req->q->queuedata;
> struct Scsi_Host *shost = sdev->host;
> struct scatterlist *sg;
> - int ret;
>
> scsi_init_command(sdev, cmd);
>
> @@ -1933,10 +1930,7 @@ static int scsi_mq_prep_fn(struct request *req)
>
> blk_mq_start_request(req);
>
> - ret = scsi_setup_cmnd(sdev, req);
> - if (ret != BLK_STS_OK)
> - cmd->flags &= ~SCMD_INITIALIZED;
> - return ret;
> + return scsi_setup_cmnd(sdev, req);
> }
>
> static void scsi_mq_done(struct scsi_cmnd *cmd)
>
Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>

--
Damien Le Moal
Western Digital Research