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a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1681489843; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc; bh=c+unp6injjwLp32rDRhFKdS15pYib3N33LpCMho7UDw=; b=tLLNUNn2IybA12zVsUJc/Wcbt3VorXkST75UUn9vq56G0ASHyaO6NmAx/tpBs4WP3+GVXe BZr11lVUYB0Yd5AQ== From: Thomas Gleixner To: LKML Cc: Peter Zijlstra , Valentin Schneider , Dennis Zhou , Tejun Heo , Christoph Lameter , Dave Chinner , Yury Norov , Andy Shevchenko , Rasmus Villemoes , Ye Bin , linux-mm@kvack.org Subject: [patch 0/3] lib/percpu_counter, cpu/hotplug: Cure the cpu_dying_mask woes Date: Fri, 14 Apr 2023 18:30:42 +0200 (CEST) X-Rspamd-Queue-Id: 7D1BC40029 X-Stat-Signature: nek33jqjzygfs6g3zc91bfkory3k8tcd X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1681489845-67614 X-HE-Meta: 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 nkLcY9GZ Jp0FgDVkXgbV9dXBPXPtCB0CQSBTxg6eRu4T0m3J+PbwaLSkoix+xYYPjAke+IVjU4tNiy0H0rbTFrxeXGC+jOtxAAI6J/e9xJ/AtoUj0VwKKDz1pb+SouJChdh4Bdu73CPndtyLK9tNNKZfMOYSHqxrDXs+fsQ8P5QQEF6hZ4X6ar4V9h5pZSHleFevqohWCBaSNrYReM/SfEWAMNWYeIVhRu26JzR/hzRu+1m7MfweiYga4x1Pk+Gns0g== 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: Hi! The cpu_dying_mask is not only undocumented but also to some extent a misnomer. It's purpose is to capture the last direction of a cpu_up() or cpu_down() operation taking eventual rollback operations into account. cpu_dying mask is not really useful for general consumption. The cpu_dying_mask bits are sticky even after cpu_up() or cpu_down() completes. A recent fix to plug a race in the per CPU counter code picked cpu_dying_mask to cure it. Unfortunately this does not work as the author probably expected and the behaviour of cpu_dying_mask is not easy to change without breaking the only other and initial user, the scheduler. This series addresses this by: 1) Reworking the per CPU counter hotplug mechanism so the race is fully plugged without using cpu_dying_mask 2) Replacing the cpu_dying_mask logic with hotplug core internal state which is exposed to the scheduler with a properly documented function. The series is also available from git: git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git smp/dying_mask Thanks tglx --- include/linux/cpuhotplug.h | 2 - include/linux/cpumask.h | 21 ---------------- kernel/cpu.c | 45 +++++++++++++++++++++++++++++------ kernel/sched/core.c | 4 +-- kernel/smpboot.h | 2 + lib/percpu_counter.c | 57 +++++++++++++++++++-------------------------- 6 files changed, 67 insertions(+), 64 deletions(-)