summaryrefslogtreecommitdiff
path: root/kernel
diff options
context:
space:
mode:
authorSergey Senozhatsky <sergey.senozhatsky@gmail.com>2016-03-17 14:21:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-17 15:09:34 -0700
commit6b97a20d3a7909daa06625d4440c2c52d7bf08d7 (patch)
treeaa794a72f34aceddfaacea169feec753460ab889 /kernel
parenta8199371afc27946d72f0d53e938e78d2ea0bae3 (diff)
downloadlinux-6b97a20d3a7909daa06625d4440c2c52d7bf08d7.tar.gz
printk: set may_schedule for some of console_trylock() callers
console_unlock() allows to cond_resched() if its caller has set `console_may_schedule' to 1, since 8d91f8b15361 ("printk: do cond_resched() between lines while outputting to consoles"). The rules are: -- console_lock() always sets `console_may_schedule' to 1 -- console_trylock() always sets `console_may_schedule' to 0 However, console_trylock() callers (among them is printk()) do not always call printk() from atomic contexts, and some of them can cond_resched() in console_unlock(), so console_trylock() can set `console_may_schedule' to 1 for such processes. For !CONFIG_PREEMPT_COUNT kernels, however, console_trylock() always sets `console_may_schedule' to 0. It's possible to drop explicit preempt_disable()/preempt_enable() in vprintk_emit(), because console_unlock() and console_trylock() are now smart enough: a) console_unlock() does not cond_resched() when it's unsafe (console_trylock() takes care of that) b) console_unlock() does can_use_console() check. Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Reviewed-by: Petr Mladek <pmladek@suse.com> Cc: Jan Kara <jack@suse.com> Cc: Tejun Heo <tj@kernel.org> Cc: Kyle McMartin <kyle@kernel.org> Cc: Dave Jones <davej@codemonkey.org.uk> Cc: Calvin Owens <calvinowens@fb.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/printk/printk.c23
1 files changed, 14 insertions, 9 deletions
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2523332bd998..a6d023c3b852 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1758,20 +1758,12 @@ asmlinkage int vprintk_emit(int facility, int level,
if (!in_sched) {
lockdep_off();
/*
- * Disable preemption to avoid being preempted while holding
- * console_sem which would prevent anyone from printing to
- * console
- */
- preempt_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())
console_unlock();
- preempt_enable();
lockdep_on();
}
@@ -2122,7 +2114,20 @@ int console_trylock(void)
return 0;
}
console_locked = 1;
- console_may_schedule = 0;
+ /*
+ * When PREEMPT_COUNT disabled we can't reliably detect if it's
+ * safe to schedule (e.g. calling printk while holding a spin_lock),
+ * because preempt_disable()/preempt_enable() are just barriers there
+ * and preempt_count() is always 0.
+ *
+ * RCU read sections have a separate preemption counter when
+ * PREEMPT_RCU enabled thus we must take extra care and check
+ * rcu_preempt_depth(), otherwise RCU read sections modify
+ * preempt_count().
+ */
+ console_may_schedule = !oops_in_progress &&
+ preemptible() &&
+ !rcu_preempt_depth();
return 1;
}
EXPORT_SYMBOL(console_trylock);