linux-kernel - [PATCH 11/11] smp: Enhance and precise the role & requirements of __smp_call_function

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Message-Id: <1391876320-25068-12-git-send-email-fweisbec@gmail.com>
Date:	Sat,  8 Feb 2014 17:18:40 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...nel.org>, Jan Kara <jack@...e.cz>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: [PATCH 11/11] smp: Enhance and precise the role & requirements of __smp_call_function_single()

Be more specific on the description of __smp_call_function_single().
It's actually not that much about just being able to embed a csd
in an object.

Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jan Kara <jack@...e.cz>
Cc: Jens Axboe <jens.axboe@...cle.com>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 kernel/smp.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/kernel/smp.c b/kernel/smp.c
index b767631..24cb936 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -238,13 +238,20 @@ int smp_call_function_single(int cpu, smp_call_func_t func, void *info,
 EXPORT_SYMBOL(smp_call_function_single);
 
 /**
- * __smp_call_function_single(): Run a function on a specific CPU
+ * __smp_call_function_single(): Run an asynchronous function on a
+ * 			         specific CPU.
  * @cpu: The CPU to run on.
  * @csd: Pre-allocated and setup data structure
  *
- * Like smp_call_function_single(), but allow caller to pass in a
- * pre-allocated data structure. Useful for embedding @data inside
- * other structures, for instance.
+ * Like smp_call_function_single(), but the call is asynchonous and
+ * can thus be done from contexts with disabled interrupts.
+ *
+ * The caller passes his own pre-allocated data structure
+ * (ie: embedded in an object) and is responsible for synchronizing it
+ * such that the IPIs performed on the @csd are strictly serialized.
+ *
+ * NOTE: Be careful, there is unfortunately no current debugging facility to
+ * validate the correctness of this serialization.
  */
 int __smp_call_function_single(int cpu, struct call_single_data *csd)
 {
-- 
1.8.3.1

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