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Message-ID: <570548DD.60103@gmail.com> Date: Wed, 6 Apr 2016 13:35:25 -0400 From: Bastien Philbert <bastienphilbert@...il.com> To: James Bottomley <jejb@...ux.vnet.ibm.com>, Julian Calaby <julian.calaby@...il.com> Cc: "Martin K. Petersen" <martin.petersen@...cle.com>, linux-scsi <linux-scsi@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] csiostor: Fix backwards locking in the function __csio_unreg_rnode On 2016-04-06 01:28 PM, James Bottomley wrote: > On Wed, 2016-04-06 at 13:23 -0400, Bastien Philbert wrote: >> >> On 2016-04-06 01:14 PM, James Bottomley wrote: >>> On Wed, 2016-04-06 at 10:36 -0400, Bastien Philbert wrote: >>>> >>>> On 2016-04-06 10:24 AM, James Bottomley wrote: >>>>> On Wed, 2016-04-06 at 10:11 -0400, Bastien Philbert wrote: >>>>>> >>>>>> On 2016-04-06 09:38 AM, James Bottomley wrote: >>>>>>> On Wed, 2016-04-06 at 09:21 -0400, Bastien Philbert wrote: >>>>>>>> >>>>>>>> On 2016-04-06 03:48 AM, Julian Calaby wrote: >>>>>>>>> Hi Bastien, >>>>>>>>> >>>>>>>>> On Wed, Apr 6, 2016 at 7:19 AM, Bastien Philbert >>>>>>>>> <bastienphilbert@...il.com> wrote: >>>>>>>>>> This fixes backwards locking in the function >>>>>>>>>> __csio_unreg_rnode >>>>>>>>>> to >>>>>>>>>> properly lock before the call to the function >>>>>>>>>> csio_unreg_rnode >>>>>>>>>> and >>>>>>>>>> not unlock with spin_unlock_irq as this would not >>>>>>>>>> allow >>>>>>>>>> the >>>>>>>>>> proper >>>>>>>>>> protection for concurrent access on the shared >>>>>>>>>> csio_hw >>>>>>>>>> structure >>>>>>>>>> pointer hw. In addition switch the locking after the >>>>>>>>>> critical >>>>>>>>>> region >>>>>>>>>> function call to properly unlock instead with >>>>>>>>>> spin_unlock_irq >>>>>>>>>> on >>>>>>>>>> >>>>>>>>>> Signed-off-by: Bastien Philbert < >>>>>>>>>> bastienphilbert@...il.com> >>>>>>>>>> --- >>>>>>>>>> drivers/scsi/csiostor/csio_rnode.c | 4 ++-- >>>>>>>>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>>>>>>>> >>>>>>>>>> diff --git a/drivers/scsi/csiostor/csio_rnode.c >>>>>>>>>> b/drivers/scsi/csiostor/csio_rnode.c >>>>>>>>>> index e9c3b04..029a09e 100644 >>>>>>>>>> --- a/drivers/scsi/csiostor/csio_rnode.c >>>>>>>>>> +++ b/drivers/scsi/csiostor/csio_rnode.c >>>>>>>>>> @@ -580,9 +580,9 @@ __csio_unreg_rnode(struct >>>>>>>>>> csio_rnode >>>>>>>>>> *rn) >>>>>>>>>> ln->last_scan_ntgts--; >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> - spin_unlock_irq(&hw->lock); >>>>>>>>>> - csio_unreg_rnode(rn); >>>>>>>>>> spin_lock_irq(&hw->lock); >>>>>>>>>> + csio_unreg_rnode(rn); >>>>>>>>>> + spin_unlock_irq(&hw->lock); >>>>>>>>> >>>>>>>>> Are you _certain_ this is correct? This construct >>>>>>>>> usually >>>>>>>>> appears >>>>>>>>> when >>>>>>>>> a function has a particular lock held, then needs to >>>>>>>>> unlock >>>>>>>>> it >>>>>>>>> to >>>>>>>>> call >>>>>>>>> some other function. Are you _certain_ that this isn't >>>>>>>>> the >>>>>>>>> case? >>>>>>>>> >>>>>>>>> Thanks, >>>>>>>>> >>>>>>>> Yes I am pretty certain this is correct. I checked the >>>>>>>> paths >>>>>>>> that >>>>>>>> called this function >>>>>>>> and it was weired that none of them gradded the spinlock >>>>>>>> before >>>>>>>> hand. >>>>>>> >>>>>>> That's not good enough. If your theory is correct, lockdep >>>>>>> should >>>>>>> be >>>>>>> dropping an already unlocked assertion in this codepath ... >>>>>>> do >>>>>>> you >>>>>>> see >>>>>>> this? >>>>>>> >>>>>>> James >>>>>>> >>>>>>> >>>>>> Yes I do. >>>>> >>>>> You mean you don't see the lockdep assert, since you're asking >>>>> to >>>>> drop the patch? >>>>> >>>>>> For now just drop the patch but I am still concerned that we >>>>>> are >>>>>> double unlocking here. >>>>> >>>>> Really, no. The pattern in the code indicates the lock is >>>>> expected >>>>> to be held. This can be wrong (sometimes code moves or people >>>>> forget), but if it is wrong we'll get an assert about unlock of >>>>> an >>>>> already unlocked lock. If there's no assert, the lock is held >>>>> on >>>>> entry and the code is correct. >>>>> >>>>> You're proposing patches based on misunderstandings of the code >>>>> which aren't backed up by actual issues and wasting everyone's >>>>> time >>>>> to look at them. Please begin with the hard evidence of a >>>>> problem >>>>> first, so post the lockdep assert in the changelog so we know >>>>> there's a real problem. >>>>> >>>>> James >>>>> >>>> Certainly James. I think I just got carried away with the last >>>> few >>>> patches :(. >>> >>> Is this Nick Krause? An email reply that Martin forwarded but the >>> list didn't pick up (because it had a html part) suggests this. >>> What you're doing is what got you banned from LKML the last time: >>> sending patches without evidence there's a problem or understanding >>> the code you're patching. Repeating the behaviour under a new >>> identity isn't going to help improve your standing. >>> >>> James >>> >> No I am not Nick Krause. I am just aware of how he got banned a few >> years ago. That email was a mistake by typo and was hoping nobody >> picked it up as they would then believe I was Nick Krause. > > Hm, OK, but currently you are repeating his behaviour ... please don't > send any more patches until they're about real problems backed by > actual data. > > Thanks, > > James > > Ok sure I do have one patch that I tested and it worked for me but wasn't sure if I am just trampling over the actual bug. If you would like me to send the patch and you can tell me if I am right please let me known. Sorry about the other patches, Bastien
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