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Subject[RFC PATCH] printk: Use ACCESS_ONCE() instead of a volatile type
Date
Remove volatile type qualifier and use ACCESS_ONCE() in its place for each
access. Using volatile is not recommended as documented in
Documentation/volatile-considered-harmful.txt.

Here logbuf_cpu is a local variable and it is not clear how it is being accessed
concurrently. We should remove volatile accesses entirely here, but for now make
a safer change of using ACCESS_ONCE().

Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
kernel/printk/printk.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e748971..4790191 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1624,7 +1624,7 @@ asmlinkage int vprintk_emit(int facility, int level,
int printed_len = 0;
bool in_sched = false;
/* cpu currently holding logbuf_lock in this function */
- static volatile unsigned int logbuf_cpu = UINT_MAX;
+ static unsigned int logbuf_cpu = UINT_MAX;

if (level == LOGLEVEL_SCHED) {
level = LOGLEVEL_DEFAULT;
@@ -1641,7 +1641,7 @@ asmlinkage int vprintk_emit(int facility, int level,
/*
* Ouch, printk recursed into itself!
*/
- if (unlikely(logbuf_cpu == this_cpu)) {
+ if (unlikely(ACCESS_ONCE(logbuf_cpu) == this_cpu)) {
/*
* If a crash is occurring during printk() on this CPU,
* then try to get the crash message out but make sure
@@ -1659,7 +1659,7 @@ asmlinkage int vprintk_emit(int facility, int level,

lockdep_off();
raw_spin_lock(&logbuf_lock);
- logbuf_cpu = this_cpu;
+ ACCESS_ONCE(logbuf_cpu) = this_cpu;

if (unlikely(recursion_bug)) {
static const char recursion_msg[] =
@@ -1754,7 +1754,7 @@ asmlinkage int vprintk_emit(int facility, int level,
dict, dictlen, text, text_len);
}

- logbuf_cpu = UINT_MAX;
+ ACCESS_ONCE(logbuf_cpu) = UINT_MAX;
raw_spin_unlock(&logbuf_lock);
lockdep_on();
local_irq_restore(flags);
--
1.9.1


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