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Message-ID: <20160117142332.GA543@swordfish>
Date: Sun, 17 Jan 2016 23:23:32 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Tejun Heo <tj@...nel.org>, Jan Kara <jack@...e.com>,
Petr Mladek <pmladek@...e.com>,
Kyle McMartin <kyle@...nel.org>,
Dave Jones <davej@...emonkey.org.uk>,
Calvin Owens <calvinowens@...com>, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH -next 2/2] printk: set may_schedule for some of
console_trylock callers
On (01/17/16 23:11), Sergey Senozhatsky wrote:
[..]
> console_locked = 1;
> - console_may_schedule = 0;
> + console_may_schedule = !(oops_in_progress ||
> + irqs_disabled() ||
> + in_atomic(),
^^^^ fat fingers, obviously. ||
> + rcu_preempt_depth());
sorry.
===8<===8<===
console_unlock() allows to cond_resched() if its caller has
set `console_may_schedule' to 1 (this functionality present
since commit '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()) are
not necessarily executing in atomic contexts, and some of them
can cond_resched() in console_unlock(). So console_trylock()
can set `console_may_schedule' to 0 only if cond_resched() is
invalid in the current context, and set it to 1 otherwise.
The patch also drops explicit preempt_disable()/preempt_enable()
calls in vprintk_emit().
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
V2: rcu_preempt_depth() on preempt RCU kernels
kernel/printk/printk.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ae641d7..9ac05e0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1777,20 +1777,12 @@ 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_for_printk())
console_unlock();
- preempt_enable();
lockdep_on();
}
@@ -2123,7 +2115,10 @@ int console_trylock(void)
return 0;
}
console_locked = 1;
- console_may_schedule = 0;
+ console_may_schedule = !(oops_in_progress ||
+ irqs_disabled() ||
+ in_atomic() ||
+ rcu_preempt_depth());
return 1;
}
EXPORT_SYMBOL(console_trylock);
--
2.7.0
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