On Fri, Feb 06, 2015 at 10:16:25PM +0000, Mathieu Desnoyers wrote: > ----- Original Message ----- > > From: "Greg Kroah-Hartman" <[email protected]> > > To: "Mathieu Desnoyers" <[email protected]> > > Cc: "Pranith Kumar" <[email protected]>, "Huang Ying" > > <[email protected]>, "LKML" > > <[email protected]>, "Paul McKenney" > > <[email protected]>, "David Howells" <[email protected]> > > Sent: Friday, February 6, 2015 10:03:59 AM > > Subject: Re: [PATCH] llist: Fix missing memory barrier > > > > On Fri, Feb 06, 2015 at 02:12:32PM +0000, Mathieu Desnoyers wrote: > > > ----- Original Message ----- > > > > From: "Pranith Kumar" <[email protected]> > > > > To: "Mathieu Desnoyers" <[email protected]> > > > > Cc: "Huang Ying" <[email protected]>, "LKML" > > > > <[email protected]>, "Paul McKenney" > > > > <[email protected]>, "David Howells" <[email protected]> > > > > Sent: Thursday, February 5, 2015 10:44:07 PM > > > > Subject: Re: [PATCH] llist: Fix missing memory barrier > > > > > > > > Hi Mathieu, > > > > > > > > On Thu, Feb 5, 2015 at 10:06 PM, Mathieu Desnoyers > > > > <[email protected]> wrote: > > > > > A smp_read_barrier_depends() appears to be missing in > > > > > llist_del_first(). > > > > > It should only matter for Alpha in practice. Adding it after the check > > > > > of entry against NULL allows skipping the barrier in a common case. > > > > > > > > We recently decided on using lockless_dereference() instead of > > > > hard-coding smp_read_barrier_depends()[1]. The advantage is that > > > > lockless_dereference() clearly shows what loads are being ordered. > > > > Could you resend the patch using that API? > > > > > > Since llist.h has been introduced prior to 3.18, I'm wondering if > > > it would be worthwhile to submit 2 patches for the purpose of > > > backporting to stable branches: > > > > > > 1) Fix introducing smp_read_barrier_depends() (for master and > > > stable branches) > > > 2) Move master from smp_read_barrier_depends() to > > > lockless_dereference(), > > > > > > Thoughts ? > > > > Yes, why? What code needs these new apis? > > The subsystems using llist.h in master: IRQ, smp core code, > vmalloc, scsi, the block layer, some filesystems... and more. > grep for "llist.h" to see the complete list of users. > > My question was mainly on how to do the fix process-wise: post-3.18, > it implies using the new lockless_dereference() API. pre-3.18, we > need to use smp_read_barrier_depends(). > > As Peter Hurley suggested, using the new API for master and 3.18 > seems like the right approach. Then the backports to stable branches > can, if needed, use smp_read_barrier_depends() instead. Is that > OK with you ?
Sounds fine to me. greg k-h -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
