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Commit 608873ca authored by Jan Kara's avatar Jan Kara Committed by Linus Torvalds
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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.

[akpm@linux-foundation.org: fix have_callable_console() comment]
Signed-off-by: default avatarJan Kara <jack@suse.cz>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ca1d432a

kernel/printk/printk.c

+21 −33
Original line number Diff line number Diff line
@@ -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 (!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 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)

		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();