Subject: + printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch added to -mm tree
To: jack@xxxxxxx
From: akpm@xxxxxxxxxxxxxxxxxxxx
Date: Wed, 23 Apr 2014 13:58:50 -0700
The patch titled
Subject: printk: release lockbuf_lock before calling console_trylock_for_printk()
has been added to the -mm tree. Its filename is
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
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------------------------------------------------------
From: Jan Kara <jack@xxxxxxx>
Subject: printk: release lockbuf_lock before calling console_trylock_for_printk()
There's no reason to hold lockbuf_lock when entering
console_trylock_for_printk().
The first thing this function does is to call down_trylock(console_sem)
and if that fails it immediately unlocks lockbuf_lock. So lockbuf_lock
isn't needed for that branch. When down_trylock() succeeds, the rest of
console_trylock() is OK without lockbuf_lock (it is called without it from
other places), and the only remaining thing in
console_trylock_for_printk() is can_use_console() call. For that call
console_sem is enough (it iterates all consoles and checks CON_ANYTIME
flag).
So we drop logbuf_lock before entering console_trylock_for_printk() which
simplifies the code.
Signed-off-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/printk/printk.c | 49 +++++++++++++--------------------------
1 file changed, 17 insertions(+), 32 deletions(-)
diff -puN kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk kernel/printk/printk.c
--- a/kernel/printk/printk.c~printk-release-lockbuf_lock-before-calling-console_trylock_for_printk
+++ a/kernel/printk/printk.c
@@ -249,9 +249,6 @@ static char __log_buf[__LOG_BUF_LEN] __a
static char *log_buf = __log_buf;
static u32 log_buf_len = __LOG_BUF_LEN;
-/* cpu currently holding logbuf_lock */
-static volatile unsigned int logbuf_cpu = UINT_MAX;
-
/* human readable text of the record */
static char *log_text(const struct printk_log *msg)
{
@@ -1410,36 +1407,22 @@ static inline int can_use_console(unsign
* messages from a 'printk'. Return true (and with the
* console_lock held, and 'console_locked' set) if it
* is successful, false otherwise.
- *
- * This gets called with the 'logbuf_lock' spinlock held and
- * interrupts disabled. It should return with 'lockbuf_lock'
- * released but interrupts still disabled.
*/
static int console_trylock_for_printk(unsigned int cpu)
- __releases(&logbuf_lock)
{
- int retval = 0, wake = 0;
-
- if (console_trylock()) {
- retval = 1;
-
- /*
- * If we can't use the console, we need to release
- * the console semaphore by hand to avoid flushing
- * the buffer. We need to hold the console semaphore
- * in order to do this test safely.
- */
- if (!can_use_console(cpu)) {
- console_locked = 0;
- wake = 1;
- retval = 0;
- }
- }
- logbuf_cpu = UINT_MAX;
- raw_spin_unlock(&logbuf_lock);
- if (wake)
+ if (!console_trylock())
+ return 0;
+ /*
+ * If we can't use the console, we need to release the console
+ * semaphore by hand to avoid flushing the buffer. We need to hold the
+ * console semaphore in order to do this test safely.
+ */
+ if (!can_use_console(cpu)) {
+ console_locked = 0;
up(&console_sem);
- return retval;
+ return 0;
+ }
+ return 1;
}
int printk_delay_msec __read_mostly;
@@ -1572,6 +1555,9 @@ asmlinkage int vprintk_emit(int facility
unsigned long flags;
int this_cpu;
int printed_len = 0;
+ /* cpu currently holding logbuf_lock in this function */
+ static volatile unsigned int logbuf_cpu = UINT_MAX;
+
boot_delay_msec(level);
printk_delay();
@@ -1694,13 +1680,12 @@ asmlinkage int vprintk_emit(int facility
dict, dictlen, text, text_len);
}
+ logbuf_cpu = UINT_MAX;
+ raw_spin_unlock(&logbuf_lock);
/*
* Try to acquire and then immediately release the console semaphore.
* The release will print out buffers and wake up /dev/kmsg and syslog()
* users.
- *
- * The console_trylock_for_printk() function will release 'logbuf_lock'
- * regardless of whether it actually gets the console semaphore or not.
*/
if (console_trylock_for_printk(this_cpu))
console_unlock();
_
Patches currently in -mm which might be from jack@xxxxxxx are
origin.patch
fanotify-fan_mark_flush-avoid-having-to-provide-a-fake-invalid-fd-and-path.patch
fanotify-create-fan_access-event-for-readdir.patch
fs-notify-markc-trivial-cleanup.patch
fs-mpagec-forgotten-write_sync-in-case-of-data-integrity-write.patch
printk-split-code-for-making-free-space-in-the-log-buffer.patch
printk-ignore-too-long-messages.patch
printk-split-message-size-computation.patch
printk-shrink-too-long-messages.patch
printk-return-really-stored-message-length.patch
printk-remove-outdated-comment.patch
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk.patch
printk-release-lockbuf_lock-before-calling-console_trylock_for_printk-fix.patch
printk-enable-interrupts-before-calling-console_trylock_for_printk.patch
printk-remove-separate-printk_sched-buffers-and-use-printk-buf-instead.patch
linux-next.patch
mm-add-strictlimit-knob-v2.patch
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