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Thu, 26 Mar 2026 13:09:11 -0700 (PDT) Received: from gourry-fedora-PF4VCD3F ([2620:10d:c091:500::2:e5e8]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50b9237a40asm31637111cf.21.2026.03.26.13.09.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Mar 2026 13:09:11 -0700 (PDT) Date: Thu, 26 Mar 2026 15:09:09 -0500 From: Gregory Price To: Matthew Wilcox Cc: linux-mm@kvack.org, akpm@linux-foundation.org, hughd@google.com, david@kernel.org, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, baolin.wang@linux.alibaba.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, stable@vger.kernel.org Subject: Re: [PATCH] mm/shmem: use invalidate_lock to fix hole-punch race Message-ID: References: <20260326162611.693539-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: B3F031C0010 X-Stat-Signature: 9bj1yus4qrbhujnwbbwkdqwickmemi88 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1774555752-730555 X-HE-Meta: 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 8+tCvjAH FZyqRnjqg39FEW5iM/3h6OO1/vMk5Z/ugJr2JmD5ywdcfUNi+kmf8624LgOsxm4j3Nm+VHtUhQT3K28p7a6Ez3keqdk07j2GscHjLqL+4qnt6crQzjxL9A8KlLKt4YWRl82bq8au2LIjTahzvgEQPpZ6mmKpEzhnDH7hb3ofDaJ/k/czlWQp4YsfRKHrONOK8F9GR1VEyDBVbZr7Ev6MZEM38GW1C/rLjYriWCumKC028zICfC+jO4+KbX+9ki0AjnlRrtFnEmDBALSIUznJgg+Y8R+nmhKFu+mpGZgDaRjEM3D1zzemGIOANSNyaLgMybivOjFjznAzpno2Xx4owmeErWBSMQuc77Ra9khHD1UJ5L6Zy2S/yXUHIjDGPxj5twOHxFiw+viYjA8gVBM0fDyDGR7W7uq1uMFAoxoXAWag1vAA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Mar 26, 2026 at 07:21:21PM +0000, Matthew Wilcox wrote: > On Thu, Mar 26, 2026 at 11:26:11AM -0500, Gregory Price wrote: > > This also requires removing the rcu_read_lock() from > > do_fault_around() so that .map_pages may use sleeping locks. > > NACK. > > ->map_pages() is called when VM asks to map easy accessible pages. > Filesystem should find and map pages associated with offsets from "start_pgoff" > till "end_pgoff". ->map_pages() is called with the RCU lock held and must > not block. If it's not possible to reach a page without blocking, > filesystem should skip it. Filesystem should use set_pte_range() to setup > page table entry. Pointer to entry associated with the page is passed in > "pte" field in vm_fault structure. Pointers to entries for other offsets > should be calculated relative to "pte". > Hm, I follow. I was originally thinking this was scoping issue given we take the rcu_read_lock shortly after the call anyway, but I see. If the invalidate lock ends up being needed then i could leave rcu and just use trylock/fallback to fault. But I need to test a few things, nothing else protects filemap_map_pages with the invalidate lock at the moment but only shmem appears broken. ~Gregory