On Tue 2018-04-03 14:19:43, wen.yan...@zte.com.cn wrote:
> On the other hand,queue_lock is big, looping doing something under spinlock 
> may locked many things and taking a long time, may cause some problems.
> So This code needs to be optimized later:
> scsi_request_fn()
> {
>       for (;;) {
>               int rtn;
>               /*
>                * get next queueable request.  We do this early to make sure
>                * that the request is fully prepared even if we cannot
>                * accept it.
>                */
>               req = blk_peek_request(q);
>               if (!req)
>                       break;
>               if (unlikely(!scsi_device_online(sdev))) {
>                       sdev_printk(KERN_ERR, sdev,
>                                   "rejected I/O to offline device\n");
>                       scsi_kill_request(req, q);
>                       continue;
>                       ^^^^^^^^^ still under spinlock
>               }

I wonder if the following might be the best solution after all:

                if (unlikely(!scsi_device_online(sdev))) {
                        scsi_kill_request(req, q);

                         * printk() might take a while on slow consoles.
                         * Prevent solftlockups by releasing the lock.
                        sdev_printk(KERN_ERR, sdev,
                                    "rejecting I/O to offline device\n");

I see that the lock is released also in several other situations.
Therefore it looks safe. Also handling too many requests without
releasing the lock seems to be a bad idea in general. I think
that this solution was already suggested earlier.

Please, note that I moved scsi_kill_request() up. It looks natural
to remove it from the queue before we release the queue lock.

Best Regards,

BTW: Your mail had strange formatting. Please, try to avoid using

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