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[SCSI] avoid useless free_list lock roundtrips 

Avoid hitting the host-wide free_list lock unless we need to put a command
back onto the freelist.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
This commit is contained in:
Christoph Hellwig 2014-02-20 14:20:53 -08:00 committed by James Bottomley
parent df03c3f628
commit 44b93b59d5
1 changed files with 6 additions and 5 deletions
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11
drivers/scsi/scsi.c
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@ -320,13 +320,14 @@ void __scsi_put_command(struct Scsi_Host *shost, struct scsi_cmnd *cmd,
{
unsigned long flags;
/* changing locks here, don't need to restore the irq state */
spin_lock_irqsave(&shost->free_list_lock, flags);
if (unlikely(list_empty(&shost->free_list))) {
list_add(&cmd->list, &shost->free_list);
cmd = NULL;
spin_lock_irqsave(&shost->free_list_lock, flags);
if (list_empty(&shost->free_list)) {
list_add(&cmd->list, &shost->free_list);
cmd = NULL;
}
spin_unlock_irqrestore(&shost->free_list_lock, flags);
}
spin_unlock_irqrestore(&shost->free_list_lock, flags);
if (likely(cmd != NULL))
scsi_pool_free_command(shost->cmd_pool, cmd);