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b=iS73GSEOVBGj8srjQKqXxORp8aFyAUqqJrJieP4bSt+uz80QDAlDkQr+C+dTHzVec n1WAekPJ/ujc0WiehjMBtxpcA0iQNxVNFcC4gKAwjPVZjQSkEeE6Xtwo2KhHRoAyB3 P0b0lol4VrgCn1uKfPTgI6ZtCRcORPz0UHuoEoIc= Date: Thu, 18 Jan 2024 13:59:41 -0800 From: Andrew Morton To: Lokesh Gidra Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, selinux@vger.kernel.org, surenb@google.com, kernel-team@android.com, aarcange@redhat.com, peterx@redhat.com, david@redhat.com, axelrasmussen@google.com, bgeffon@google.com, willy@infradead.org, jannh@google.com, kaleshsingh@google.com, ngeoffray@google.com Subject: Re: [PATCH] userfaultfd: fix mmap_changing checking in mfill_atomic_hugetlb Message-Id: <20240118135941.c7795d52881f486aa21aeea8@linux-foundation.org> In-Reply-To: <20240117223729.1444522-1-lokeshgidra@google.com> References: <20240117223729.1444522-1-lokeshgidra@google.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 70A951A0021 X-Stat-Signature: gxtwwexsa7ohh7ajjzdpi16otgunmuqa X-HE-Tag: 1705615187-649756 X-HE-Meta: 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 4h/a4xCR qA0tjlDntlQtQA8WENLmlnhQK3GLpSlyOieD9D6ZBrjVfFVZN/gjQ+5N3ThD0ueqvcRNpRfzMwcc9k7rFRbVKLVroCf7tmfH/Ujw45megj+pAYLWy9YwPQY3D3V3JCd+BsG4sGKUEWi8njhvLY9EJSjd43x1AIaByc8+lQ+S+vx/HX5LMZ+wVJCcxEnSErIinI6Fy3KiwcL65kjCrDjPJWaDJZ/H8rA7nJgm8hKQDYIqjtxClt666r9NuKUjWwy58vRiEjXV/JEnpkcooNb7GkFZJNcQWorh/CZkLlzN480OfEWM= 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: List-Subscribe: List-Unsubscribe: On Wed, 17 Jan 2024 14:37:29 -0800 Lokesh Gidra wrote: > In mfill_atomic_hugetlb(), mmap_changing isn't being checked > again if we drop mmap_lock and reacquire it. When the lock is not held, > mmap_changing could have been incremented. This is also inconsistent > with the behavior in mfill_atomic(). Thanks. Could you and reviewers please consider - what might be the userspace-visible runtime effects? - Should the fix be backported into earlier kernels? - A suitable Fixes: target?