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Tue, 14 May 2024 21:03:44 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id /kVBKbDRQ2Y5KAAAD6G6ig (envelope-from ); Tue, 14 May 2024 21:03:44 +0000 Date: Tue, 14 May 2024 23:03:39 +0200 From: Oscar Salvador To: =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= Cc: Alexandre Ghiti , Albert Ou , David Hildenbrand , Palmer Dabbelt , Paul Walmsley , linux-riscv@lists.infradead.org, =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Andrew Bresticker , Chethan Seshadri , Lorenzo Stoakes , Santosh Mamila , Sivakumar Munnangi , Sunil V L , linux-kernel@vger.kernel.org, linux-mm@kvack.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v2 5/8] riscv: mm: Take memory hotplug read-lock during kernel page table dump Message-ID: References: <20240514140446.538622-1-bjorn@kernel.org> <20240514140446.538622-6-bjorn@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240514140446.538622-6-bjorn@kernel.org> X-Rspamd-Action: no action X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 4DD5CC001B X-Stat-Signature: n5z4p79uo1p5oc1pe46u47r9hder4kqy X-Rspam-User: X-HE-Tag: 1715720627-306906 X-HE-Meta: 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 M+8qEhRf ezH2eB0rqGrBbPEftL6q7k7DEqTX9WPweb0NUCAkZoY8akB50JAgX7cgVhF846NBJxmDpS/LGhjQpwJiv4EMFBs2S252pxnfPOaqqlRx2cA2xa0REO5M/w0I/8m2YGqNXpCU7JpEmXx+8zAQCwFAQA+cLnL+FrifMDmdrtQD1RaJqZve2D9Hy7Ayx1hP2gkKrwgcvLRhewLXCYvZx/o/JMhMMHgbD4aMfJFoT1tNcWW/jd/CxkLAgHKnzeTBpCc8OXsozREXi2LQRm/Cdld52m0nBfn5gJ+f/BZ7/ 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 Tue, May 14, 2024 at 04:04:43PM +0200, Björn Töpel wrote: > From: Björn Töpel > > During memory hot remove, the ptdump functionality can end up touching > stale data. Avoid any potential crashes (or worse), by holding the > memory hotplug read-lock while traversing the page table. > > This change is analogous to arm64's commit bf2b59f60ee1 ("arm64/mm: > Hold memory hotplug lock while walking for kernel page table dump"). > > Signed-off-by: Björn Töpel Reviewed-by: Oscar Salvador funny enough, it seems arm64 and riscv are the only ones holding the hotplug lock here. I think we have the same problem on the other arches as well (at least on x86_64 that I can see). If we happen to finally need the lock in those, I would rather have a centric function in the generic mm code with the locking and then calling an arch specific ptdump_show function, so the lock is not scattered. But that is another story. -- Oscar Salvador SUSE Labs