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Howlett" Cc: "Matthew Wilcox (Oracle)" Subject: [PATCH] mm: Always downgrade mmap_lock if requested Date: Thu, 29 Jun 2023 20:14:14 +0100 Message-Id: <20230629191414.1215929-1-willy@infradead.org> X-Mailer: git-send-email 2.37.1 MIME-Version: 1.0 X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 4B2C7C000D X-Stat-Signature: f6gnej1pifwmo3q68cyaw5bf59q3gj6d X-Rspam-User: X-HE-Tag: 1688066059-697348 X-HE-Meta: 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 Sb5fqjov 5+5ewIX/GMa8GfUtm9j/uKuzJVZu507kmxXYGTIqiSbXLVwBOnoXDxE4ZXaaqntgm9muHdU/JcVTQBBYZSyXSjzmRhYU29D28/5wiARhYf/b3sBhP5ldu/fAa0CLM8An4TTnmrUVo7rHo1HRpJKuMa2hA93pKGxrZjRwfoxb3yF82qQvv/Pr+1Bpc976e4pNtzOvtZ0ukVc9tEjm23gUKXIz/Gx1IIM6YevZp X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Now that stack growth must always hold the mmap_lock for write, we can always downgrade the mmap_lock to read and safely unmap pages from the page table, even if we're next to a stack. Signed-off-by: Matthew Wilcox (Oracle) --- mm/mmap.c | 15 ++------------- 1 file changed, 2 insertions(+), 13 deletions(-) diff --git a/mm/mmap.c b/mm/mmap.c index 9b5188b65800..82efaca58ca2 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -2550,19 +2550,8 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma, mm->locked_vm -= locked_vm; mm->map_count -= count; - /* - * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or - * VM_GROWSUP VMA. Such VMAs can change their size under - * down_read(mmap_lock) and collide with the VMA we are about to unmap. - */ - if (downgrade) { - if (next && (next->vm_flags & VM_GROWSDOWN)) - downgrade = false; - else if (prev && (prev->vm_flags & VM_GROWSUP)) - downgrade = false; - else - mmap_write_downgrade(mm); - } + if (downgrade) + mmap_write_downgrade(mm); /* * We can free page tables without write-locking mmap_lock because VMAs