Re: [PATCH v2] PM: hibernate: Fix a bug in copying the zero bitmap to safe pages

[Rafael J. Wysocki]

On Wed, Oct 4, 2023 at 2:19 PM Brian Geffon <bgeffon@xxxxxxxxxx> wrote:
>
> On Wed, Oct 4, 2023 at 1:01 AM Pavankumar Kondeti
> <quic_pkondeti@xxxxxxxxxxx> wrote:
> >
> > The following crash is observed 100% of the time during resume from
> > the hibernation on a x86 QEMU system.
> >
> > [   12.931887]  ? __die_body+0x1a/0x60
> > [   12.932324]  ? page_fault_oops+0x156/0x420
> > [   12.932824]  ? search_exception_tables+0x37/0x50
> > [   12.933389]  ? fixup_exception+0x21/0x300
> > [   12.933889]  ? exc_page_fault+0x69/0x150
> > [   12.934371]  ? asm_exc_page_fault+0x26/0x30
> > [   12.934869]  ? get_buffer.constprop.0+0xac/0x100
> > [   12.935428]  snapshot_write_next+0x7c/0x9f0
> > [   12.935929]  ? submit_bio_noacct_nocheck+0x2c2/0x370
> > [   12.936530]  ? submit_bio_noacct+0x44/0x2c0
> > [   12.937035]  ? hib_submit_io+0xa5/0x110
> > [   12.937501]  load_image+0x83/0x1a0
> > [   12.937919]  swsusp_read+0x17f/0x1d0
> > [   12.938355]  ? create_basic_memory_bitmaps+0x1b7/0x240
> > [   12.938967]  load_image_and_restore+0x45/0xc0
> > [   12.939494]  software_resume+0x13c/0x180
> > [   12.939994]  resume_store+0xa3/0x1d0
> >
> > The commit being fixed introduced a bug in copying the zero bitmap
> > to safe pages. A temporary bitmap is allocated with PG_ANY flag in
> > prepare_image() to make a copy of zero bitmap after the unsafe pages
> > are marked. Freeing this temporary bitmap with PG_UNSAFE_KEEP later
> > results in an inconsistent state of unsafe pages. Since free bit is
> > left as is for this temporary bitmap after free, these pages are
> > treated as unsafe pages when they are allocated again. This results
> > in incorrect calculation of the number of pages pre-allocated for the
> > image.
> >
> > nr_pages = (nr_zero_pages + nr_copy_pages) - nr_highmem - allocated_unsafe_pages;
> >
> > The allocate_unsafe_pages is estimated to be higher than the actual
> > which results in running short of pages in safe_pages_list. Hence the
> > crash is observed in get_buffer() due to NULL pointer access of
> > safe_pages_list.
> >
> > Fix this issue by creating the temporary zero bitmap from safe pages
> > (free bit not set) so that the corresponding free bits can be cleared while
> > freeing this bitmap.
> >
> > Cc: stable <stable@xxxxxxxxxx>
> > Fixes: 005e8dddd497 ("PM: hibernate: don't store zero pages in the image file")
> > Suggested-by:: Brian Geffon <bgeffon@xxxxxxxxxx>
> > Signed-off-by: Pavankumar Kondeti <quic_pkondeti@xxxxxxxxxxx>
>
> Reviewed-by: Brian Geffon <bgeffon@xxxxxxxxxx>

Applied as 6.7 material, but without the Cc: stable tag that is (a)
invalid (there should be vger.kernel.org in the host part) and (b)
unnecessary AFAICS.

Thanks!