Petr Mladek 257ab44311 printk: Correctly handle preemption in console_unlock() ... Some console drivers code calls console_conditional_schedule() that looks at @console_may_schedule. The value must be cleared when the drivers are called from console_unlock() with interrupts disabled. But rescheduling is fine when the same code is called, for example, from tty operations where the console semaphore is taken via console_lock(). This is why @console_may_schedule is cleared before calling console drivers. The original value is stored to decide if we could sleep between lines. Now, @console_may_schedule is not cleared when we call console_trylock() and jump back to the "again" goto label. This has become a problem, since the commit 6b97a20d3a ("printk: set may_schedule for some of console_trylock() callers"). @console_may_schedule might get enabled now. There is also the opposite problem. console_lock() can be called only from preemptive context. It can always enable scheduling in the console code. But console_trylock() is not able to detect it when CONFIG_PREEMPT_COUNT is disabled. Therefore we should use the original @console_may_schedule value after re-acquiring the console semaphore in console_unlock(). This patch solves both problems by moving the "again" goto label. Alternative solution was to clear and restore the value around call_console_drivers(). Then console_conditional_schedule() could be used also inside console_unlock(). But there was a potential race with console_flush_on_panic() as reported by Sergey Senozhatsky. That function should be called only where there is only one CPU and with interrupts disabled. But better be on the safe side because stopping CPUs might fail. Fixes: 6b97a20d3a ("printk: set may_schedule for some of console_trylock() callers") Link: http://lkml.kernel.org/r/1490372045-22288-1-git-send-email-pmladek@suse.com Suggested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jiri Slaby <jslaby@suse.cz> Cc: linux-fbdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Petr Mladek <pmladek@suse.com>		2017-04-04 14:08:01 +02:00
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braille.c	printk: fix parsing of "brl=" option	2016-08-26 17:39:35 -07:00
braille.h	printk: move braille console support into separate braille.[ch] files	2013-07-31 14:41:03 -07:00
console_cmdline.h	console: Fix console name size mismatch	2015-03-07 03:39:55 +01:00
internal.h	printk: report lost messages in printk safe/nmi contexts	2017-02-08 13:50:05 +01:00
Makefile	printk: introduce per-cpu safe_print seq buffer	2017-02-08 11:07:11 +01:00
printk_safe.c	printk: report lost messages in printk safe/nmi contexts	2017-02-08 13:50:05 +01:00
printk.c	printk: Correctly handle preemption in console_unlock()	2017-04-04 14:08:01 +02:00