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printk: release lockbuf_lock before calling console_trylock_for_printk()

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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.

[akpm@linux-foundation.org: fix have_callable_console() comment]
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jan Kara 2014-06-04 16:11:35 -07:00 committed by Linus Torvalds
parent ca1d432ad8
commit 608873cacb
1 changed files with 21 additions and 33 deletions
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54
kernel/printk/printk.c
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@ -249,9 +249,6 @@ static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN);
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)
{
@ -1380,7 +1377,10 @@ static void zap_locks(void)
sema_init(&console_sem, 1);
}
/* Check if we have any console registered that can be called early in boot. */
/*
* Check if we have any console that is capable of printing while cpu is
* booting or shutting down. Requires console_sem.
*/
static int have_callable_console(void)
{
struct console *con;
@ -1410,36 +1410,22 @@ static inline int can_use_console(unsigned int cpu)
* 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 +1558,9 @@ asmlinkage int vprintk_emit(int facility, int level,
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 +1683,12 @@ asmlinkage int vprintk_emit(int facility, int level,
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();