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Subject: printk: Make rt aware
From: Thomas Gleixner <tglx@linutronix.de>
Date: Wed, 19 Sep 2012 14:50:37 +0200
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.19/older/patches-4.19.13-rt10.tar.xz
Drop the lock before calling the console driver and do not disable
interrupts while printing to a serial console.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
kernel/printk/printk.c | 33 ++++++++++++++++++++++++++++++---
1 file changed, 30 insertions(+), 3 deletions(-)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1617,6 +1617,7 @@ SYSCALL_DEFINE3(syslog, int, type, char
return do_syslog(type, buf, len, SYSLOG_FROM_READER);
}
+#ifndef CONFIG_PREEMPT_RT_FULL
/*
* Special console_lock variants that help to reduce the risk of soft-lockups.
* They allow to pass console_lock to another printk() call using a busy wait.
@@ -1757,6 +1758,15 @@ static int console_trylock_spinning(void
return 1;
}
+#else
+
+static int console_trylock_spinning(void)
+{
+ return console_trylock();
+}
+
+#endif
+
/*
* Call the console drivers, asking them to write out
* log_buf[start] to log_buf[end - 1].
@@ -1772,6 +1782,7 @@ static void call_console_drivers(const c
if (!console_drivers)
return;
+ migrate_disable();
for_each_console(con) {
if (exclusive_console && con != exclusive_console)
continue;
@@ -1787,6 +1798,7 @@ static void call_console_drivers(const c
else
con->write(con, text, len);
}
+ migrate_enable();
}
int printk_delay_msec __read_mostly;
@@ -1978,20 +1990,30 @@ asmlinkage int vprintk_emit(int facility
/* If called from the scheduler, we can not call up(). */
if (!in_sched) {
+ int may_trylock = 1;
+
+#ifdef CONFIG_PREEMPT_RT_FULL
+ /*
+ * we can't take a sleeping lock with IRQs or preeption disabled
+ * so we can't print in these contexts
+ */
+ if (!(preempt_count() == 0 && !irqs_disabled()))
+ may_trylock = 0;
+#endif
/*
* Disable preemption to avoid being preempted while holding
* console_sem which would prevent anyone from printing to
* console
*/
- preempt_disable();
+ migrate_disable();
/*
* Try to acquire and then immediately release the console
* semaphore. The release will print out buffers and wake up
* /dev/kmsg and syslog() users.
*/
- if (console_trylock_spinning())
+ if (may_trylock && console_trylock_spinning())
console_unlock();
- preempt_enable();
+ migrate_enable();
}
wake_up_klogd();
@@ -2444,6 +2466,10 @@ void console_unlock(void)
console_seq++;
raw_spin_unlock(&logbuf_lock);
+#ifdef CONFIG_PREEMPT_RT_FULL
+ printk_safe_exit_irqrestore(flags);
+ call_console_drivers(ext_text, ext_len, text, len);
+#else
/*
* While actively printing out messages, if another printk()
* were to occur on another CPU, it may wait for this one to
@@ -2462,6 +2488,7 @@ void console_unlock(void)
}
printk_safe_exit_irqrestore(flags);
+#endif
if (do_cond_resched)
cond_resched();
|
