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Wed, 24 Dec 2025 12:38:16 -0500 (EST) From: Mathieu Desnoyers To: Andrew Morton Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Mark Brown , linux-mm@kvack.org Subject: [PATCH 1/1] tsacct: Skip all kernel threads Date: Wed, 24 Dec 2025 12:38:10 -0500 Message-Id: <20251224173810.648699-2-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20251224173810.648699-1-mathieu.desnoyers@efficios.com> References: <20251224173810.648699-1-mathieu.desnoyers@efficios.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: a5ny9ockfrg7q4jgi6winf667iqpye8d X-Rspam-User: X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: BE85D1C0002 X-HE-Tag: 1766597897-684704 X-HE-Meta: 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 ynuM61bF Cp7eMoHHjL9UyWz3JtxXxQbDSajcYaYgo9P+q7YCagpAfjzPi2Vg5m+kjwexF1mnI2HhJkm05pSCy44MsPR4wApFcoSrDYzd91z2rQjS8B5leXSWaAS3eExxPaF34k7A1kHRitSTx/vhlSYxziSSjV0eezdZcu8T3LeSXX5LMIt7uqQ3js9mbxomVpd8HGaDi6zItbcU8lvOUl/UESssshantl8xh3W46SITUv9WWKVniZMPusDdjKxrHQX55bC8MCS++TXOJ9hgKfsxKKFHI9JRZDxExXaHeN6KF46J3HWpTPmFq1CW8DM0OQuasStyCiYXhvXuQYKRp7BpLWBgHDHX76L9MX69Y6IxFd1y4gUpgRmxsxKerR8Wb27PXkFXN5IiD3t77AFOoa+V4GdaS3Dg5jd3RMf+82/ZkHwlUHIPdH82NyN93QkXzXqqTMZAtUPvE 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: When we hit acct_account_cputime within a irq handler over a kthread that happens to use a userspace mm, we end up summing up the mm's RSS into the tsk acct_rss_mem1, which eventually decays. I don't see a good rationale behind tracking the mm's rss in that way when a kthread use a userspace mm temporarily through use_mm. It causes issues with init_mm and efi_mm which only partially initialize their mm_struct when introducing the new hierarchical percpu counters to replace RSS counters, which requires a pointer dereference when reading the approximate counter sum. The current percpu counters simply load a zeroed atomic counter, which happen to work. Skip all kernel threads in acct_account_cputime(), not just those that happen to have a NULL mm. This is a preparation step before introducing the hierarchical percpu counters. Signed-off-by: Mathieu Desnoyers Cc: Andrew Morton Cc: Mark Brown Cc: linux-mm@kvack.org --- kernel/tsacct.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/tsacct.c b/kernel/tsacct.c index 6ea2f6363b90..5c153106e642 100644 --- a/kernel/tsacct.c +++ b/kernel/tsacct.c @@ -125,7 +125,7 @@ static void __acct_update_integrals(struct task_struct *tsk, { u64 time, delta; - if (!likely(tsk->mm)) + if (unlikely(!tsk->mm || (tsk->flags & PF_KTHREAD))) return; time = stime + utime; -- 2.39.5