Messages in this thread | | | Date | Thu, 10 Jul 2014 08:06:17 +0200 | From | Christoph Hellwig <> | Subject | Re: [PATCH 09/14] scsi: fix the {host,target,device}_blocked counter mess |
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On Wed, Jul 09, 2014 at 01:12:17PM +0200, Hannes Reinecke wrote: > Hmm. I guess there is a race window between > atomic_read() and atomic_set(). > Doesn't this cause issues when someone calls atomic_set() just before the > call to atomic_read?
There is a race window just _after_ the atomic_read, but it's harmless. The whole _blocked scheme is a backoff to avoid resubmitting I/O all the time when the HBA or target returned a busy status. If we race an incorrectly reset it we will submit I/O and just get a busy indicator again.
On the other hand doing the atomic_set all the time introduces three atomic in the I/O completion part that are entirely pointless most of the time.
I guess I should add something like this as a comment to the code..
Note that the old code didn't use any sort of synchronization either.
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