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Suppose a folio is under migration, and khugepaged is also trying to collapse it. collapse_pte_mapped_thp() will retrieve the folio from the page cache via filemap_lock_folio(), thus taking a reference on the folio and sleeping on the folio lock, since the lock is held by the migration path. Migration will then fail in __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of such a race happening (leading to migration failure) by bailing out if we detect a PMD is marked with a migration entry. This fixes the migration-shared-anon-thp testcase failure on Apple M3. Note that, this is not a "fix" since it only reduces the chance of interference of khugepaged with migration, wherein both the kernel functionalities are deemed "best-effort". Link: https://lkml.kernel.org/r/20250704040417.63826-1-dev.jain@arm.com Signed-off-by: Dev Jain <dev.jain@arm.com> Acked-by: David Hildenbrand <david@redhat.com> Acked-by: Oscar Salvador <osalvador@suse.de> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com> Reviewed-by: Zi Yan <ziy@nvidia.com> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Barry Song <baohua@kernel.org> Cc: Liam Howlett <liam.howlett@oracle.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Mariano Pache <npache@redhat.com> Cc: Ryan Roberts <ryan.roberts@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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.