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Patch series " Remove XA_ZERO from error recovery of dup_mmap()", v3. It is possible that the dup_mmap() call fails on allocating or setting up a vma after the maple tree of the oldmm is copied. Today, that failure point is marked by inserting an XA_ZERO entry over the failure point so that the exact location does not need to be communicated through to exit_mmap(). However, a race exists in the tear down process because the dup_mmap() drops the mmap lock before exit_mmap() can remove the partially set up vma tree. This means that other tasks may get to the mm tree and find the invalid vma pointer (since it's an XA_ZERO entry), even though the mm is marked as MMF_OOM_SKIP and MMF_UNSTABLE. To remove the race fully, the tree must be cleaned up before dropping the lock. This is accomplished by extracting the vma cleanup in exit_mmap() and changing the required functions to pass through the vma search limit. Any other tree modifications would require extra cycles which should be spent on freeing memory. This does run the risk of increasing the possibility of finding no vmas (which is already possible!) in code that isn't careful. The final four patches are to address the excessive argument lists being passed between the functions. Using the struct unmap_desc also allows some special-case code to be removed in favour of the struct setup differences. This patch (of 11): pgtables.h defines a fallback for ceiling and floor of the page tables within the CONFIG_MMU section. Moving the definitions to outside the CONFIG_MMU allows for using them in generic code. [akpm@linux-foundation.org: remove stray newline, per SeongJae] Link: https://lkml.kernel.org/r/20260121164946.2093480-1-Liam.Howlett@oracle.com Link: https://lkml.kernel.org/r/20260121164946.2093480-2-Liam.Howlett@oracle.com Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Suggested-by: SeongJae Park <sj@kernel.org> Cc: Baoquan He <bhe@redhat.com> Cc: Barry Song <baohua@kernel.org> Cc: Chris Li <chrisl@kernel.org> Cc: David Hildenbrand <david@kernel.org> Cc: Jann Horn <jannh@google.com> Cc: Kairui Song <kasong@tencent.com> Cc: Kemeng Shi <shikemeng@huaweicloud.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Nhat Pham <nphamcs@gmail.com> Cc: Pedro Falcato <pfalcato@suse.de> Cc: Suren Baghdasaryan <surenb@google.com> Cc: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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