On 14:29, Neil Brown wrote: > > Are you worried about another CPU setting conf->pending_bio_list.head > > to != NULL after the if statement? If that's an issue I think also > > the original patch is problematic because the same might happen after > > the final spin_unlock_irq() but but before flush_pending_writes() > > returns zero. > > No. I'm worried that another CPU might set > conf->pending_bio_list.head *before* the if statement, but it isn't > seen by this CPU because of the lack of memory barriers. The spinlock > ensures that the memory state is consistent. But is that enough to avoid the deadlock? I think the following scenario would be possible with the code in the original patch: // suppose conf->pending_bio_list.head==NULL ATM CPU0: int rv = 0; spin_lock_irq(&conf->device_lock); if (conf->pending_bio_list.head) // false spin_unlock_irq(&conf->device_lock); CPU1: conf->pending_bio_list.head = something; CPU0: return rv; // zero Andre -- The only person who always got his work done by Friday was Robinson Crusoe
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