linux-kernel - Re: [PATCH v3 02/11] scsi: scsi_debug: Don't iter all shosts in clear_luns_changed_on

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Date:   Tue, 28 Mar 2023 19:39:05 -0400
From:   Douglas Gilbert <dgilbert@...erlog.com>
To:     John Garry <john.g.garry@...cle.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        bvanassche@....org
Subject: Re: [PATCH v3 02/11] scsi: scsi_debug: Don't iter all shosts in
 clear_luns_changed_on_target()

On 2023-03-27 03:43, John Garry wrote:
> In clear_luns_changed_on_target(), we iter all devices for all shosts to
> conditionally clear the SDEBUG_UA_LUNS_CHANGED flag in the per-device
> uas_bm.
> 
> One condition to see whether we clear the flag is to test whether the host
> for the device under consideration is the same as the matching device's
> (devip) host. This check will only ever pass for devices for the same
> shost, so only iter the devices for the matching device shost.
> 
> We can now drop the spinlock'ing of the sdebug_host_list_lock in the same
> function. This will allow us to use a mutex instead of the spinlock for
> the global shost lock, as clear_luns_changed_on_target() could be called
> in non-blocking context, in scsi_debug_queuecommand() -> make_ua() ->
> clear_luns_changed_on_target() (which is why required a spinlock).
> 
> Signed-off-by: John Garry <john.g.garry@...cle.com>
Acked-by: Douglas Gilbert <dgilbert@...erlog.com

Thanks.

> ---
>   drivers/scsi/scsi_debug.c | 13 +++++--------
>   1 file changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 782515abca2c..eba6eca81e84 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -1063,18 +1063,15 @@ static void all_config_cdb_len(void)
>   
>   static void clear_luns_changed_on_target(struct sdebug_dev_info *devip)
>   {
> -	struct sdebug_host_info *sdhp;
> +	struct sdebug_host_info *sdhp = devip->sdbg_host;
>   	struct sdebug_dev_info *dp;
>   
> -	spin_lock(&sdebug_host_list_lock);
> -	list_for_each_entry(sdhp, &sdebug_host_list, host_list) {
> -		list_for_each_entry(dp, &sdhp->dev_info_list, dev_list) {
> -			if ((devip->sdbg_host == dp->sdbg_host) &&
> -			    (devip->target == dp->target))
> -				clear_bit(SDEBUG_UA_LUNS_CHANGED, dp->uas_bm);
> +	list_for_each_entry(dp, &sdhp->dev_info_list, dev_list) {
> +		if ((devip->sdbg_host == dp->sdbg_host) &&
> +		    (devip->target == dp->target)) {
> +			clear_bit(SDEBUG_UA_LUNS_CHANGED, dp->uas_bm);
>   		}
>   	}
> -	spin_unlock(&sdebug_host_list_lock);
>   }
>   
>   static int make_ua(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)