________________________________________ From: Matthew Wilcox [matthew@xxxxxx] Sent: Tuesday, July 05, 2011 10:14 AM To: Desai, Kashyap Cc: Matthew Wilcox; linux-scsi@xxxxxxxxxxxxxxx; DL-MPT Fusion Linux Subject: Re: [PATCH] mpt2sas: Remove queuecommand wrapper On Tue, Jul 05, 2011 at 10:16:25AM +0530, Desai, Kashyap wrote: > Matthew, I am fine with the patch, but just wanted to double check we do have included changes related to below conversation. > Mpt2sas and mptsas driver wants IRQ and preemption disable when it enter in to qcmd callback. > > http://140.211.166.79/mailarchive/linux-scsi/2010/12/23/6887919 The piece I believe you're referring to: YES. ! That is my concern.. > I have gone through another round of code walkthrough (for mpt2sas and mptfusion) to \ > find out dependency w.r.t new host lock less mode. In my opinion, w/ interrupts \ > disable is a good ideal. (Earlier, I mentioned that mpt2sas is safe even if \ > interrupts are enabled) In real scenario, *preemption* disable is more IMP for \ > mpt2sas/mptfusion driver than interrupts disable. > e.a if scsih_qcmd_xxx has executed half of the code and (due to preemption is not \ > disable for the same CPU), Scheduler can execute any other process on the SAME cpu \ > (Though IRQ is disable). Consider Error handling is kicked off on the same CPU and as \ > part of EH, it executed HBA reset. As part of HBA reset Driver has return back all \ > pending Scsi command to mid-layer, and once control come back to original \ > scsih_qcmd_xxx LLD drive will see bad results (Kernel crash/Data corruption/h/w hung \ > or anything critical.....) I don't believe this scenario can happen. Error handling will not commence until all commands are returned to the midlayer, which requires that queuecommand is no longer running. I was able to see this scenario when I intially started doing code review. Since host_lock is removed Error handling can remove code from queuecommand anytime ( I asssume preemption is not disable, only IRQ is disable).. I am almost sure if we are planning to remove host_lock from SML, we at least need irq and preemption disable for mpt2sas and mptfusion to work properly. I am not sure we have done those changes in SML ? -- 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
