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

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Date:   Tue, 3 Oct 2023 08:38:17 +0530
From:   Pavan Kondeti <quic_pkondeti@...cinc.com>
To:     Brian Geffon <bgeffon@...gle.com>
CC:     Pavankumar Kondeti <quic_pkondeti@...cinc.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
        <kernel@...cinc.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PM: hibernate: Fix a bug in copying the zero bitmap to
 safe pages

On Sat, Sep 30, 2023 at 07:37:13AM -0400, Brian Geffon wrote:
> On Fri, Sep 29, 2023 at 1:31 PM Pavankumar Kondeti
> <quic_pkondeti@...cinc.com> wrote:
> >
> Hi Pavankumar,
> 
> > 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 in prepare_image()
> > to make a copy of zero bitmap after the unsafe pages are marked.
> > Freeing this temporary bitmap 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.
> 
> Rafael pulled https://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git/commit/?h=linux-next&id=f0c7183008b41e92fa676406d87f18773724b48b
> which addresses the null pointer dereference which regardless
> shouldn't be touching the list directly and should be using
> __get_safe_page().

Thanks for pointing me to this. I have verified hibernation by pulling this
commit to v6.6-rc3 and it works as expected.

This commit is currently queued for v6.7, can it be included in next -rc or 
we have to apply the patch I have sent to make sure that hibernation works on
v6.6 when it gets released.

> 
> >
> > Fixes: 005e8dddd497 ("PM: hibernate: don't store zero pages in the image file")
> > Signed-off-by: Pavankumar Kondeti <quic_pkondeti@...cinc.com>

Thanks,
Pavan