Message-ID: <CAJuCfpHUZBkGtu8CL=5cxNMtJa4iNyJ8gBVu2Ho_WOXCRzzfTA@mail.gmail.com>
Date: Thu, 22 Aug 2024 15:50:27 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hao Ge <hao.ge@...ux.dev>
Cc: Miaohe Lin <linmiaohe@...wei.com>, kent.overstreet@...ux.dev, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, Hao Ge <gehao@...inos.cn>, stable@...r.kernel.org, 
	nao.horiguchi@...il.com, akpm@...ux-foundation.org, pasha.tatashin@...een.com, 
	david@...hat.com
Subject: Re: [PATCH] codetag: debug: mark codetags for pages which
 transitioned from being poison to unpoison as empty

On Thu, Aug 22, 2024 at 2:46 AM Hao Ge <hao.ge@...ux.dev> wrote:
>
> Hi Miaohe
>
>
> Thank you for taking the time to review this patch.
>
>
> On 8/22/24 16:04, Miaohe Lin wrote:
> > On 2024/8/22 10:58, Hao Ge wrote:
> >> From: Hao Ge <gehao@...inos.cn>
> >>
> > Thanks for your patch.
> >
> >> The PG_hwpoison page will be caught and isolated on the entrance to
> >> the free buddy page pool. so,when we clear this flag and return it
> >> to the buddy system,mark codetags for pages as empty.
> >>
> > Is below scene cause the problem?
> >
> > 1. Pages are allocated. pgalloc_tag_add() will be called when prep_new_page().
> >
> > 2. Pages are hwpoisoned. memory_failure() will set PG_hwpoison flag and pgalloc_tag_sub()
> > will be called when pages are caught and isolated on the entrance to buddy.

Hi Folks,
Thanks for reporting this! Could you please describe in more details
how memory_failure() ends up calling pgalloc_tag_sub()? It's not
obvious to me which path leads to pgalloc_tag_sub(), so I must be
missing something.
On a conceptual level I want to understand if the page isolated in
this manner should be considered freed or not. If it shouldn't be
considered free then I think the right fix would be to avoid
pgalloc_tag_sub() when this isolation happens.
Thanks,
Suren.

> >
> > 3. unpoison_memory cleared flags and sent the pages to buddy. pgalloc_tag_sub() will be
> > called again in free_pages_prepare().
> >
> > So there is a imbalance that pgalloc_tag_add() is called once and pgalloc_tag_sub() is called twice?
> As you said, that's exactly the case.
> >
> > If so, let's think about more complicated scene:
> >
> > 1. Same as above.
> >
> > 2. Pages are hwpoisoned. But memory_failure() fails to handle it. So PG_hwpoison flag is set
> > but pgalloc_tag_sub() is not called (pages are not sent to buddy).
> >
> > 3. unpoison_memory cleared flags and calls clear_page_tag_ref() without calling pgalloc_tag_sub()
> > first. Will this cause problem?
> >
> > Though this should be really rare...
> >
> > Thanks.
> > .
>
> Great, I didn't anticipate this scenario.
>
> When we call clear_page_tag_ref() without calling pgalloc_tag_sub(),
>
> It will cause exceptions in|tag->counters->bytes|and|tag->counters->calls|.
>
> We can add a layer of protection to handle it
>
> The pseudocode is as follows:
>
> if (mem_alloc_profiling_enabled()) {
>          union codetag_ref *ref = get_page_tag_ref(page);
>
>          if (ref) {
>              if( ref->ct != NULL && !is_codetag_empty(ref))
>              {
>                  tag = ct_to_alloc_tag(ref->ct);
>                  this_cpu_sub(tag->counters->bytes, bytes);
>                  this_cpu_dec(tag->counters->calls);
>              }
>              set_codetag_empty(ref);
>              put_page_tag_ref(ref);
>          }
> }
>
> Hi Suren and Kent
>
> Do you have any suggestions for this? If it's okay, I'll add comments
> and include this pseudocode in|clear_page_tag_ref|.
>
> >> It was detected by [1] and the following WARN occurred:
> >>
> >> [  113.930443][ T3282] ------------[ cut here ]------------
> >> [  113.931105][ T3282] alloc_tag was not set
> >> [  113.931576][ T3282] WARNING: CPU: 2 PID: 3282 at ./include/linux/alloc_tag.h:130 pgalloc_tag_sub.part.66+0x154/0x164
> >> [  113.932866][ T3282] Modules linked in: hwpoison_inject fuse ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ebtable_broute ip6table_nat ip6table_man4
> >> [  113.941638][ T3282] CPU: 2 UID: 0 PID: 3282 Comm: madvise11 Kdump: loaded Tainted: G        W          6.11.0-rc4-dirty #18
> >> [  113.943003][ T3282] Tainted: [W]=WARN
> >> [  113.943453][ T3282] Hardware name: QEMU KVM Virtual Machine, BIOS unknown 2/2/2022
> >> [  113.944378][ T3282] pstate: 40400005 (nZcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> >> [  113.945319][ T3282] pc : pgalloc_tag_sub.part.66+0x154/0x164
> >> [  113.946016][ T3282] lr : pgalloc_tag_sub.part.66+0x154/0x164
> >> [  113.946706][ T3282] sp : ffff800087093a10
> >> [  113.947197][ T3282] x29: ffff800087093a10 x28: ffff0000d7a9d400 x27: ffff80008249f0a0
> >> [  113.948165][ T3282] x26: 0000000000000000 x25: ffff80008249f2b0 x24: 0000000000000000
> >> [  113.949134][ T3282] x23: 0000000000000001 x22: 0000000000000001 x21: 0000000000000000
> >> [  113.950597][ T3282] x20: ffff0000c08fcad8 x19: ffff80008251e000 x18: ffffffffffffffff
> >> [  113.952207][ T3282] x17: 0000000000000000 x16: 0000000000000000 x15: ffff800081746210
> >> [  113.953161][ T3282] x14: 0000000000000000 x13: 205d323832335420 x12: 5b5d353031313339
> >> [  113.954120][ T3282] x11: ffff800087093500 x10: 000000000000005d x9 : 00000000ffffffd0
> >> [  113.955078][ T3282] x8 : 7f7f7f7f7f7f7f7f x7 : ffff80008236ba90 x6 : c0000000ffff7fff
> >> [  113.956036][ T3282] x5 : ffff000b34bf4dc8 x4 : ffff8000820aba90 x3 : 0000000000000001
> >> [  113.956994][ T3282] x2 : ffff800ab320f000 x1 : 841d1e35ac932e00 x0 : 0000000000000000
> >> [  113.957962][ T3282] Call trace:
> >> [  113.958350][ T3282]  pgalloc_tag_sub.part.66+0x154/0x164
> >> [  113.959000][ T3282]  pgalloc_tag_sub+0x14/0x1c
> >> [  113.959539][ T3282]  free_unref_page+0xf4/0x4b8
> >> [  113.960096][ T3282]  __folio_put+0xd4/0x120
> >> [  113.960614][ T3282]  folio_put+0x24/0x50
> >> [  113.961103][ T3282]  unpoison_memory+0x4f0/0x5b0
> >> [  113.961678][ T3282]  hwpoison_unpoison+0x30/0x48 [hwpoison_inject]
> >> [  113.962436][ T3282]  simple_attr_write_xsigned.isra.34+0xec/0x1cc
> >> [  113.963183][ T3282]  simple_attr_write+0x38/0x48
> >> [  113.963750][ T3282]  debugfs_attr_write+0x54/0x80
> >> [  113.964330][ T3282]  full_proxy_write+0x68/0x98
> >> [  113.964880][ T3282]  vfs_write+0xdc/0x4d0
> >> [  113.965372][ T3282]  ksys_write+0x78/0x100
> >> [  113.965875][ T3282]  __arm64_sys_write+0x24/0x30
> >> [  113.966440][ T3282]  invoke_syscall+0x7c/0x104
> >> [  113.966984][ T3282]  el0_svc_common.constprop.1+0x88/0x104
> >> [  113.967652][ T3282]  do_el0_svc+0x2c/0x38
> >> [  113.968893][ T3282]  el0_svc+0x3c/0x1b8
> >> [  113.969379][ T3282]  el0t_64_sync_handler+0x98/0xbc
> >> [  113.969980][ T3282]  el0t_64_sync+0x19c/0x1a0
> >> [  113.970511][ T3282] ---[ end trace 0000000000000000 ]---
> >>
> >> Link [1]: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/syscalls/madvise/madvise11.c
> >>
> >> Fixes: a8fc28dad6d5 ("alloc_tag: introduce clear_page_tag_ref() helper function")
> >> Cc: stable@...r.kernel.org # v6.10
> >> Signed-off-by: Hao Ge <gehao@...inos.cn>
> >> ---
> >>   mm/memory-failure.c | 6 ++++++
> >>   1 file changed, 6 insertions(+)
> >>
> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> >> index 7066fc84f351..570388c41532 100644
> >> --- a/mm/memory-failure.c
> >> +++ b/mm/memory-failure.c
> >> @@ -2623,6 +2623,12 @@ int unpoison_memory(unsigned long pfn)
> >>
> >>              folio_put(folio);
> >>              if (TestClearPageHWPoison(p)) {
> >> +                    /* the PG_hwpoison page will be caught and isolated
> >> +                     * on the entrance to the free buddy page pool.
> >> +                     * so,when we clear this flag and return it to the buddy system,
> >> +                     * clear it's codetag
> >> +                     */
> >> +                    clear_page_tag_ref(p);
> >>                      folio_put(folio);
> >>                      ret = 0;
> >>              }
> >>
> >>
> Thanks
>
> BR
>
> Hao
>

Powered by blists - more mailing lists