Message ID | 20221102183336.3120536-6-vschneid@redhat.com |
---|---|
State | New |
Headers | show
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McKenney" <paulmck@kernel.org>, Steven Rostedt <rostedt@goodmis.org>, Peter Zijlstra <peterz@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Sebastian Andrzej Siewior <bigeasy@linutronix.de>, Juri Lelli <juri.lelli@redhat.com>, Daniel Bristot de Oliveira <bristot@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>, Frederic Weisbecker <frederic@kernel.org>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, Dave Hansen <dave.hansen@linux.intel.com>, "H. Peter Anvin" <hpa@zytor.com>, Marc Zyngier <maz@kernel.org>, Mark Rutland <mark.rutland@arm.com>, Russell King <linux@armlinux.org.uk>, Nicholas Piggin <npiggin@gmail.com>, Guo Ren <guoren@kernel.org>, "David S. Miller" <davem@davemloft.net> Subject: [RFC PATCH v2 7/8] smp: reword smp call IPI comment Date: Wed, 2 Nov 2022 18:33:35 +0000 Message-Id: <20221102183336.3120536-6-vschneid@redhat.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20221102182949.3119584-1-vschneid@redhat.com> References: <20221102182949.3119584-1-vschneid@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221102_113445_773700_F2467076 X-CRM114-Status: GOOD ( 15.85 ) X-Spam-Score: -0.4 (/) X-Spam-Report: Spam detection software, running on the system "bombadil.infradead.org", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: Accessing the call_single_queue hasn't involved a spinlock since 2014: 6897fc22ea01 ("kernel: use lockless list for smp_call_function_single") The llist operations (namely cmpxchg() and xchg()) provide similar ordering guarantees, update the comment to lessen confusion. 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Generic IPI sending tracepoint
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expand
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diff --git a/kernel/smp.c b/kernel/smp.c index 44fa4b9b1f46b..b96579fe08f09 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -503,9 +503,10 @@ void __smp_call_single_queue(int cpu, struct llist_node *node) #endif /* - * The list addition should be visible before sending the IPI - * handler locks the list to pull the entry off it because of - * normal cache coherency rules implied by spinlocks. + * The list addition should be visible to the target CPU when it pops + * the head of the list to pull the entry off it in the IPI handler + * because of normal cache coherency rules implied by the underlying + * llist ops. * * If IPIs can go out of order to the cache coherency protocol * in an architecture, sufficient synchronisation should be added
Accessing the call_single_queue hasn't involved a spinlock since 2014: 6897fc22ea01 ("kernel: use lockless list for smp_call_function_single") The llist operations (namely cmpxchg() and xchg()) provide similar ordering guarantees, update the comment to lessen confusion. Signed-off-by: Valentin Schneider <vschneid@redhat.com> --- kernel/smp.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)