Jan Schmidt suggested using raw_smp_processor_id() back in February, see this: http://marc.info/?t=132974687100003&r=1&w=2 Alex Shi recently suggested using preempt_disable() and preempt_enable() to solve the same issue, see this: http://marc.info/?t=133274303900003&r=1&w=2 I believe the stack traces are there in both email discussion, they occur when CONFIG_DEBUG_PREEMPT is enabled. I would rather go with the solution giving the best performance. James Bottomley is there on the discussion with Jan Schmidt, he suggested using get_cpu() and put_cpu(). Eric ________________________________________ From: Matthew Wilcox [matthew@xxxxxx] Sent: Tuesday, April 17, 2012 9:14 PM To: Nandigama, Nagalakshmi Cc: stable@xxxxxxxxxxxxxxx; linux-scsi@xxxxxxxxxxxxxxx; Prakash, Sathya; Moore, Eric; jejb@xxxxxxxxxx Subject: Re: [PATCH] [SCSI] mpt2sas : Fix unsafe using smp_processor_id() in preemptible On Tue, Apr 17, 2012 at 11:25:04AM +0530, nagalakshmi.nandigama@xxxxxxx wrote: > When CONFIG_DEBUG_PREEMPT is enabled, bug is observed in the smp_processor_id(). > This is because smp_processor_id() is not called in preempt safe condition. > > To fix this issue, use raw_smp_processor_id instead of smp_processor_id. Just so we're clear, "fix this issue" really means "paper over the warning". * NOTE: raw_smp_processor_id() is for internal use only * (smp_processor_id() is the preferred variant), but in rare * instances it might also be used to turn off false positives * (i.e. smp_processor_id() use that the debugging code reports but * which use for some reason is legal). Don't use this to hack around * the warning message, as your code might not work under PREEMPT. As far as I can tell, it's called under a lock already so should be non-preemptable ... can you share the backtrace you get? > Signed-off-by: Nagalakshmi Nandigama <nagalakshmi.nandigama@xxxxxxx> > CC: stable@xxxxxxxxxxxxxxx > --- > > diff --git a/drivers/scsi/mpt2sas/mpt2sas_base.c b/drivers/scsi/mpt2sas/mpt2sas_base.c > index 272fab7..b010be0 100644 > --- a/drivers/scsi/mpt2sas/mpt2sas_base.c > +++ b/drivers/scsi/mpt2sas/mpt2sas_base.c > @@ -1792,7 +1792,7 @@ static inline void _base_writeq(__u64 b, volatile void __iomem *addr, > static inline u8 > _base_get_msix_index(struct MPT2SAS_ADAPTER *ioc) > { > - return ioc->cpu_msix_table[smp_processor_id()]; > + return ioc->cpu_msix_table[raw_smp_processor_id()]; > } > > /** > -- > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
