On Tue, May 20, 2014 at 12:34:53PM -0700, Andrew Morton wrote:
> On Tue, 20 May 2014 16:49:00 +0100 Mel Gorman <mgorman@xxxxxxx> wrote:
>
> > Prabhakar Lad reported the following problem
> >
> > I see following issue on DA850 evm,
> > git bisect points me to
> > commit id: 975c3a671f11279441006a29a19f55ccc15fb320
> > ( mm: non-atomically mark page accessed during page cache allocation
> > where possible)
> >
> > Unable to handle kernel paging request at virtual address 30e03501
> > pgd = c68cc000
> > [30e03501] *pgd=00000000
> > Internal error: Oops: 1 [#1] PREEMPT ARM
> > Modules linked in:
> > CPU: 0 PID: 1015 Comm: network.sh Not tainted 3.15.0-rc5-00323-g975c3a6 #9
> > task: c70c4e00 ti: c73d0000 task.ti: c73d0000
> > PC is at init_page_accessed+0xc/0x24
> > LR is at shmem_write_begin+0x54/0x60
> > pc : [<c0088aa0>] lr : [<c00923e8>] psr: 20000013
> > sp : c73d1d90 ip : c73d1da0 fp : c73d1d9c
> > r10: c73d1dec r9 : 00000000 r8 : 00000000
> > r7 : c73d1e6c r6 : c694d7bc r5 : ffffffe4 r4 : c73d1dec
> > r3 : c73d0000 r2 : 00000001 r1 : 00000000 r0 : 30e03501
> > Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> > Control: 0005317f Table: c68cc000 DAC: 00000015
> > Process network.sh (pid: 1015, stack limit = 0xc73d01c0)
> >
> > pagep is set but not pointing to anywhere valid as it's an uninitialised
> > stack variable. This patch is a fix to
> > mm-non-atomically-mark-page-accessed-during-page-cache-allocation-where-possible.patch
> >
> > ...
> >
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2459,7 +2459,7 @@ ssize_t generic_perform_write(struct file *file,
> > flags |= AOP_FLAG_UNINTERRUPTIBLE;
> >
> > do {
> > - struct page *page;
> > + struct page *page = NULL;
> > unsigned long offset; /* Offset into pagecache page */
> > unsigned long bytes; /* Bytes to write to page */
> > size_t copied; /* Bytes copied from user */
>
> Well not really. generic_perform_write() only touches *page if
> ->write_begin() returned "success", which is reasonable behavior.
>
> I'd say you mucked up shmem_write_begin() - it runs
> init_page_accessed() even if shmem_getpage() returned an error. It
> shouldn't be doing that.
>
> This?
>
> From: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Subject: mm/shmem.c: don't run init_page_accessed() against an uninitialised pointer
>
> If shmem_getpage() returned an error then it didn't necessarily initialise
> *pagep. So shmem_write_begin() shouldn't be playing with *pagep in this
> situation.
>
> Fixes an oops when "mm: non-atomically mark page accessed during page
> cache allocation where possible" (quite reasonably) left *pagep
> uninitialized.
>
> Reported-by: Prabhakar Lad <prabhakar.csengg@xxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Jan Kara <jack@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxx>
--
Mel Gorman
SUSE Labs
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