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Jinjiang Tu 656eaddbc9 mm/vmscan: fix hwpoisoned large folio handling in shrink_folio_list 
commit 9f1e8cd0b7 upstream.

In shrink_folio_list(), the hwpoisoned folio may be large folio, which
can't be handled by unmap_poisoned_folio().  For THP, try_to_unmap_one()
must be passed with TTU_SPLIT_HUGE_PMD to split huge PMD first and then
retry.  Without TTU_SPLIT_HUGE_PMD, we will trigger null-ptr deref of
pvmw.pte.  Even we passed TTU_SPLIT_HUGE_PMD, we will trigger a
WARN_ON_ONCE due to the page isn't in swapcache.

Since UCE is rare in real world, and race with reclaimation is more rare,
just skipping the hwpoisoned large folio is enough.  memory_failure() will
handle it if the UCE is triggered again.

This happens when memory reclaim for large folio races with
memory_failure(), and will lead to kernel panic.  The race is as
follows:

cpu0      cpu1
 shrink_folio_list memory_failure
  TestSetPageHWPoison
  unmap_poisoned_folio
  --> trigger BUG_ON due to
  unmap_poisoned_folio couldn't
   handle large folio

[tujinjiang@huawei.com: add comment to unmap_poisoned_folio()]
  Link: https://lkml.kernel.org/r/69fd4e00-1b13-d5f7-1c82-705c7d977ea4@huawei.com
Link: https://lkml.kernel.org/r/20250627125747.3094074-2-tujinjiang@huawei.com
Signed-off-by: Jinjiang Tu <tujinjiang@huawei.com>
Fixes: 1b0449544c ("mm/vmscan: don't try to reclaim hwpoison folio")
Reported-by: syzbot+3b220254df55d8ca8a61@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/68412d57.050a0220.2461cf.000e.GAE@google.com/
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Acked-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-08-01 09:48:44 +01:00
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README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.