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Received: from authenticated-user by stravinsky.debian.org with esmtpsa (TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_256_GCM:256) (Exim 4.96) (envelope-from ) id 1wY0Vl-00AiTX-0J; Fri, 12 Jun 2026 11:57:21 +0000 Date: Fri, 12 Jun 2026 04:57:17 -0700 From: Breno Leitao To: Lance Yang Cc: catalin.marinas@arm.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, sj@kernel.org Subject: Re: [PATCH RFC] mm/kmemleak: avoid soft lockup when scanning task stacks Message-ID: References: <20260611-kmemleak-stack-resched-v1-1-d6248ade5f4a@debian.org> <20260612031605.58235-1-lance.yang@linux.dev> <6bc446b7-8e25-4add-9d72-a3c9e9191533@linux.dev> <086712c1-18bc-414a-9a7a-723b9498847a@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <086712c1-18bc-414a-9a7a-723b9498847a@linux.dev> X-Debian-User: leitao X-Rspamd-Server: rspam07 X-Rspam-User: X-Stat-Signature: dc17xy95wdgzrzwkooqzt9kwmgdb1am5 X-Rspamd-Queue-Id: 2648A180003 X-HE-Tag: 1781265446-969430 X-HE-Meta: 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 MPXNu2Zq gVDao3wJ8bI+jjwk7ANT6jwQDv/aWzTRqfjPd4TZzg5W5qC7H4ZIlMvxIj5+t98TWOwyW55aZ87Ijqvfq5l9K+3PYEyrIfGJwJLTnjgVPW1SdjlYPKJRL8THBFQELFu8lVZk9XZp1AikoyxaVKVK7D4E3NLOuD0O0c03BE/nJrXI1fvhW6jvHiGdvF22rhnAe175T1NfR2kYqWgWiPQw6mqVtzqX9rDsbcv5KjjYli8cHIN8BGnqeLrGzwphde4WJT++U Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Jun 12, 2026 at 07:22:38PM +0800, Lance Yang wrote: > > > On 2026/6/12 18:39, Breno Leitao wrote: > > On Fri, Jun 12, 2026 at 05:57:12PM +0800, Lance Yang wrote: > > > > > > If we go this route, the aborted round has to suppress reporting, reusing > > > > kmemleak's existing "scan was interrupted -> don't report" path: > > > > > > > > if (need_resched() && !kmemleak_stack_scan_break(g, p)) { > > > > aborted = true; > > > > goto unlock; > > > > } > > > > > > I'd expect the normal case to just drop RCU, cond_resched(), take RCU > > > again, see both cursors still alive, and keep walking :) > > > > > > > ... > > > > if (scan_should_stop() || aborted) > > > > return; > > > > > > And yeah, you're right. If we do lost a cursor, bailing out and > > > skipping reporting fot that incomplete root scan should be the > > > right thing, I guess :D > > > > Thanks! Under what circumstances would the cursor actually be lost? > > It should be race, but possible, that we happen to stop on g/p, > drop RCU, and one of them is gone by the time we come back. ACk, that makes sense, with that, I think this approach might be better than the original one in this patchset. Let me play with it. Thanks for the suggestion, --breno