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[193.116.117.77]) by smtp.gmail.com with ESMTPSA id f20-20020a637554000000b004df4ba1ebfesm877558pgn.66.2023.02.02.23.18.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Feb 2023 23:18:59 -0800 (PST) From: Nicholas Piggin To: Andrew Morton Cc: Nicholas Piggin , Linus Torvalds , Nadav Amit , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Catalin Marinas , Will Deacon , Rik van Riel , linux-arch@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org Subject: [PATCH v7 1/5] kthread: simplify kthread_use_mm refcounting Date: Fri, 3 Feb 2023 17:18:33 +1000 Message-Id: <20230203071837.1136453-2-npiggin@gmail.com> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20230203071837.1136453-1-npiggin@gmail.com> References: <20230203071837.1136453-1-npiggin@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org Remove the special case avoiding refcounting when the mm to be used is the same as the kernel thread's active (lazy tlb) mm. kthread_use_mm() should not be such a performance critical path that this matters much. This simplifies a later change to lazy tlb mm refcounting. Acked-by: Linus Torvalds Signed-off-by: Nicholas Piggin --- kernel/kthread.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/kernel/kthread.c b/kernel/kthread.c index f97fd01a2932..7424a1839e9a 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -1410,14 +1410,13 @@ void kthread_use_mm(struct mm_struct *mm) WARN_ON_ONCE(!(tsk->flags & PF_KTHREAD)); WARN_ON_ONCE(tsk->mm); + mmgrab(mm); + task_lock(tsk); /* Hold off tlb flush IPIs while switching mm's */ local_irq_disable(); active_mm = tsk->active_mm; - if (active_mm != mm) { - mmgrab(mm); - tsk->active_mm = mm; - } + tsk->active_mm = mm; tsk->mm = mm; membarrier_update_current_mm(mm); switch_mm_irqs_off(active_mm, mm, tsk); @@ -1434,12 +1433,9 @@ void kthread_use_mm(struct mm_struct *mm) * memory barrier after storing to tsk->mm, before accessing * user-space memory. A full memory barrier for membarrier * {PRIVATE,GLOBAL}_EXPEDITED is implicitly provided by - * mmdrop(), or explicitly with smp_mb(). + * mmdrop(). */ - if (active_mm != mm) - mmdrop(active_mm); - else - smp_mb(); + mmdrop(active_mm); } EXPORT_SYMBOL_GPL(kthread_use_mm); -- 2.37.2