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David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: a6aby6fe6nawutdfgu9ftpccq7kqg3tf X-Rspam-User: X-Rspamd-Queue-Id: 0F18F1A0006 X-Rspamd-Server: rspam06 X-HE-Tag: 1674169624-683130 X-HE-Meta: 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 OoPpIdn3 hQFznUzlZtJGhEQ6K2g9V8Kp9/Qe94Fd1OgNYxrbRA7yFbUyfk+I4hQaAIBg3NdIBtm4BrCmRP93RGZFyAOUrIMibCCZR6xfzVY1lKL84QUWUsUMUbmM91WZyGR6PTEujBduYa/3i26wIiYZiUYsHy5wDnMatUQOUks8WLWPEpl3Bke60XL+qYt/Pi1ZRM4Ti1E22YpJcXynHJKDejnvon8BImgIlmzEz3uUmQT9E42cu9oRAsWTmym9/epuVaxn/OWVi9dF3snNnbSgkTGDu38sJA/LwJguzPJvW2QNd5ycxGW2FLR/RuBSGAA== 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: On Thu, Jan 19, 2023 at 2:37 PM Peter Xu wrote: > > On Thu, Jan 05, 2023 at 10:18:33AM +0000, James Houghton wrote: > > + /* > > + * Grab the VMA lock and mapping sem for writing. This will prevent > > + * concurrent high-granularity page table walks, so that we can safely > > + * collapse and free page tables. > > + * > > + * This is the same locking that huge_pmd_unshare requires. > > + */ > > + hugetlb_vma_lock_write(vma); > > + i_mmap_lock_write(vma->vm_file->f_mapping); > > One thing I just noticed - do we need the mmap write lock here? I don't > quickly see what stops another thread from having the mmap read and walking > upon the pgtables being collapsed. Maybe. Does huge_pmd_unshare() have the same problem?