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: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5bc5447..6e1b21a 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -249,9 +249,6 @@
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 @@
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 @@
* 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 @@
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 @@
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();