Re: [PATCH] scsi: target: tcmu: fix size in calls to tcmu_flush_dcache_range

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Sep 01, 2020 at 05:58:29PM +0200, Bodo Stroesser wrote:
> On 2020-09-01 16:02, Greg KH wrote:
> > On Fri, Aug 28, 2020 at 12:03:38PM +0200, Bodo Stroesser wrote:
> >> Hi,
> >> I'm adding stable@vger.kernel.org
> >>
> >> Once again, this time really adding stable.
> >>
> >> On 2020-06-03 04:31, Martin K. Petersen wrote:
> >>> On Thu, 28 May 2020 21:31:08 +0200, Bodo Stroesser wrote:
> >>>
> >>>> 1) If remaining ring space before the end of the ring is
> >>>>       smaller then the next cmd to write, tcmu writes a padding
> >>>>       entry which fills the remaining space at the end of the
> >>>>       ring.
> >>>>       Then tcmu calls tcmu_flush_dcache_range() with the size
> >>>>       of struct tcmu_cmd_entry as data length to flush.
> >>>>       If the space filled by the padding was smaller then
> >>>>       tcmu_cmd_entry, tcmu_flush_dcache_range() is called for
> >>>>       an address range reaching behind the end of the vmalloc'ed
> >>>>       ring.
> >>>>       tcmu_flush_dcache_range() in a loop calls
> >>>>          flush_dcache_page(virt_to_page(start));
> >>>>       for every page being part of the range. On x86 the line is
> >>>>       optimized out by the compiler, as flush_dcache_page() is
> >>>>       empty on x86.
> >>>>       But I assume the above can cause trouble on other
> >>>>       architectures that really have a flush_dcache_page().
> >>>>       For paddings only the header part of an entry is relevant
> >>>>       Due to alignment rules the header always fits in the
> >>>>       remaining space, if padding is needed.
> >>>>       So tcmu_flush_dcache_range() can safely be called with
> >>>>       sizeof(entry->hdr) as the length here.
> >>>>
> >>>> [...]
> >>>
> >>> Applied to 5.8/scsi-queue, thanks!
> >>>
> >>> [1/1] scsi: target: tcmu: Fix size in calls to tcmu_flush_dcache_range
> >>>          https://git.kernel.org/mkp/scsi/c/8c4e0f212398
> >>>
> >>
> >> The full commit of this patch is:
> >>       8c4e0f212398cdd1eb4310a5981d06a723cdd24f
> >>
> >> This patch is the first of four patches that are necessary to run tcmu
> >> on ARM without crash. For details please see
> >>       https://bugzilla.kernel.org/show_bug.cgi?id=208045
> >> Upsteam commits of patches 2,3, and 4 are:
> >>     2: 3c58f737231e "scsi: target: tcmu: Optimize use of flush_dcache_page"
> >>     3: 3145550a7f8b "scsi: target: tcmu: Fix crash in tcmu_flush_dcache_range
> >> on ARM"
> >>     4: 5a0c256d96f0 "scsi: target: tcmu: Fix crash on ARM during cmd
> >> completion"
> >>
> >> Since patches 3 and 4 already were accepted for 5.8, 5.4, and 4.19, and
> >> I sent a request to add patch 2 about 1 hour ago, please consider adding
> >> this patch to 5.4 and 4.19, because without it tcmu on ARM will still
> >> crash.
> > 
> > I don't see such a request, and am confused now.
> > 
> > What exact commits do you want backported, and to what trees?
> > 
> > thanks,
> > 
> > greg k-h
> > 
> 
> Sorry for the confusion.
> 
> The subject of the request I mentioned is
>     "Re: [PATCH v2 0/2] scsi: target: tcmu: fix crashes on ARM"
> because it is for the first patch of a small series of two.
> 
> Please backport to kernels 4.19 and 5.4 (it is part of 5.8 from beginning):
>   8c4e0f212398 "scsi: target: tcmu: fix size in calls to tcmu_flush_dcache_range"
> 
> Please backport to kernels 4.19, 5.4 and 5.8:
>   3c58f737231e "scsi: target: tcmu: Optimize use of flush_dcache_page"
> 
> Backporting to 4.14 or earlier AFAICS would need more work, especially testing.
> I don't think that its worth it.

Thanks, both now queued up.

greg k-h