From: rostedt@goodmis.org (Steven Rostedt)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] ring-buffer: Replace this_cpu_*() with __this_cpu_*()
Date: Tue, 17 Mar 2015 10:40:38 -0400 [thread overview]
Message-ID: <20150317104038.312e73d1@gandalf.local.home> (raw)
In-Reply-To: <20150317101113.32f5618a@gandalf.local.home>
It has come to my attention that this_cpu_read/write are horrible on
architectures other than x86. Worse yet, they actually disable
preemption or interrupts! This caused some unexpected tracing results
on ARM.
101.356868: preempt_count_add <-ring_buffer_lock_reserve
101.356870: preempt_count_sub <-ring_buffer_lock_reserve
The ring_buffer_lock_reserve has recursion protection that requires
accessing a per cpu variable. But since preempt_disable() is traced, it
too got traced while accessing the variable that is suppose to prevent
recursion like this.
The generic version of this_cpu_read() and write() are:
#define _this_cpu_generic_read(pcp) \
({ typeof(pcp) ret__; \
preempt_disable(); \
ret__ = *this_cpu_ptr(&(pcp)); \
preempt_enable(); \
ret__; \
})
#define _this_cpu_generic_to_op(pcp, val, op) \
do { \
unsigned long flags; \
raw_local_irq_save(flags); \
*__this_cpu_ptr(&(pcp)) op val; \
raw_local_irq_restore(flags); \
} while (0)
Which is unacceptable for locations that know they are within preempt
disabled or interrupt disabled locations.
Paul McKenney stated that __this_cpu_() versions produce much better code on
other architectures than this_cpu_() does, if we know that the call is done in
a preempt disabled location.
I also changed the recursive_unlock() to use two local variables instead
of accessing the per_cpu variable twice.
Link: http://lkml.kernel.org/r/20150317114411.GE3589 at linux.vnet.ibm.com
Cc: stable at vger.kernel.org
Cc: Christoph Lameter <cl@linux.com>
Reported-by: Uwe Kleine-K?nig <u.kleine-koenig@pengutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
Changes since v1:
Use __this_cpu_*() instead of this_cpu_ptr()
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 5040d44fe5a3..363b9ec58aae 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -2679,7 +2679,7 @@ static DEFINE_PER_CPU(unsigned int, current_context);
static __always_inline int trace_recursive_lock(void)
{
- unsigned int val = this_cpu_read(current_context);
+ unsigned int val = __this_cpu_read(current_context);
int bit;
if (in_interrupt()) {
@@ -2696,18 +2696,19 @@ static __always_inline int trace_recursive_lock(void)
return 1;
val |= (1 << bit);
- this_cpu_write(current_context, val);
+ __this_cpu_write(current_context, val);
return 0;
}
static __always_inline void trace_recursive_unlock(void)
{
- unsigned int val = this_cpu_read(current_context);
+ unsigned int val = __this_cpu_read(current_context);
+ unsigned int val2;
- val--;
- val &= this_cpu_read(current_context);
- this_cpu_write(current_context, val);
+ val2 = val - 1;
+ val &= val2;
+ __this_cpu_write(current_context, val);
}
#else
next prev parent reply other threads:[~2015-03-17 14:40 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-16 21:31 [RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr() Steven Rostedt
2015-03-17 5:56 ` Christoph Lameter
2015-03-17 12:13 ` Steven Rostedt
2015-03-17 14:11 ` Steven Rostedt
2015-03-17 14:40 ` Steven Rostedt [this message]
2015-03-17 14:47 ` [PATCH v2] ring-buffer: Replace this_cpu_*() with __this_cpu_*() Uwe Kleine-König
2015-03-17 15:07 ` Steven Rostedt
2015-03-19 16:20 ` Christoph Lameter
2015-03-19 16:31 ` Steven Rostedt
2015-03-19 16:33 ` Christoph Lameter
2015-03-19 16:40 ` Steven Rostedt
2015-03-24 18:49 ` Christoph Lameter
2015-03-19 16:19 ` [RFC][PATCH] ring-buffer: Replace this_cpu_{read,write} with this_cpu_ptr() Christoph Lameter
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20150317104038.312e73d1@gandalf.local.home \
--to=rostedt@goodmis.org \
--cc=linux-arm-kernel@lists.infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).