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author | Tejun Heo <tj@kernel.org> | 2016-01-15 16:58:24 -0800 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-02-17 12:30:57 -0800 |
commit | a623f87a72de35096a9eae7cc7764d0c9533c2e9 (patch) | |
tree | ba1c30c5cbbb2ca94e124b2a150a2ee7c260673d | |
parent | bf46aa7ec7417cab8b4402dc8117e17af54f5d8e (diff) | |
download | linux-stable-a623f87a72de35096a9eae7cc7764d0c9533c2e9.tar.gz linux-stable-a623f87a72de35096a9eae7cc7764d0c9533c2e9.tar.bz2 linux-stable-a623f87a72de35096a9eae7cc7764d0c9533c2e9.zip |
printk: do cond_resched() between lines while outputting to consoles
commit 8d91f8b15361dfb438ab6eb3b319e2ded43458ff upstream.
@console_may_schedule tracks whether console_sem was acquired through
lock or trylock. If the former, we're inside a sleepable context and
console_conditional_schedule() performs cond_resched(). This allows
console drivers which use console_lock for synchronization to yield
while performing time-consuming operations such as scrolling.
However, the actual console outputting is performed while holding
irq-safe logbuf_lock, so console_unlock() clears @console_may_schedule
before starting outputting lines. Also, only a few drivers call
console_conditional_schedule() to begin with. This means that when a
lot of lines need to be output by console_unlock(), for example on a
console registration, the task doing console_unlock() may not yield for
a long time on a non-preemptible kernel.
If this happens with a slow console devices, for example a serial
console, the outputting task may occupy the cpu for a very long time.
Long enough to trigger softlockup and/or RCU stall warnings, which in
turn pile more messages, sometimes enough to trigger the next cycle of
warnings incapacitating the system.
Fix it by making console_unlock() insert cond_resched() between lines if
@console_may_schedule.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Jan Kara <jack@suse.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Kyle McMartin <kyle@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r-- | include/linux/console.h | 1 | ||||
-rw-r--r-- | kernel/panic.c | 3 | ||||
-rw-r--r-- | kernel/printk/printk.c | 35 |
3 files changed, 36 insertions, 3 deletions
diff --git a/include/linux/console.h b/include/linux/console.h index bd194343c346..ea731af2451e 100644 --- a/include/linux/console.h +++ b/include/linux/console.h @@ -150,6 +150,7 @@ extern int console_trylock(void); extern void console_unlock(void); extern void console_conditional_schedule(void); extern void console_unblank(void); +extern void console_flush_on_panic(void); extern struct tty_driver *console_device(int *); extern void console_stop(struct console *); extern void console_start(struct console *); diff --git a/kernel/panic.c b/kernel/panic.c index 4b150bc0c6c1..41e2b54f36b5 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -157,8 +157,7 @@ void panic(const char *fmt, ...) * panic() is not being callled from OOPS. */ debug_locks_off(); - console_trylock(); - console_unlock(); + console_flush_on_panic(); if (!panic_blink) panic_blink = no_blink; diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 2ce8826f1053..c048e34b177f 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -2233,13 +2233,24 @@ void console_unlock(void) static u64 seen_seq; unsigned long flags; bool wake_klogd = false; - bool retry; + bool do_cond_resched, retry; if (console_suspended) { up_console_sem(); return; } + /* + * Console drivers are called under logbuf_lock, so + * @console_may_schedule should be cleared before; however, we may + * end up dumping a lot of lines, for example, if called from + * console registration path, and should invoke cond_resched() + * between lines if allowable. Not doing so can cause a very long + * scheduling stall on a slow console leading to RCU stall and + * softlockup warnings which exacerbate the issue with more + * messages practically incapacitating the system. + */ + do_cond_resched = console_may_schedule; console_may_schedule = 0; /* flush buffered message fragment immediately to console */ @@ -2311,6 +2322,9 @@ skip: call_console_drivers(level, ext_text, ext_len, text, len); start_critical_timings(); local_irq_restore(flags); + + if (do_cond_resched) + cond_resched(); } console_locked = 0; @@ -2378,6 +2392,25 @@ void console_unblank(void) console_unlock(); } +/** + * console_flush_on_panic - flush console content on panic + * + * Immediately output all pending messages no matter what. + */ +void console_flush_on_panic(void) +{ + /* + * If someone else is holding the console lock, trylock will fail + * and may_schedule may be set. Ignore and proceed to unlock so + * that messages are flushed out. As this can be called from any + * context and we don't want to get preempted while flushing, + * ensure may_schedule is cleared. + */ + console_trylock(); + console_may_schedule = 0; + console_unlock(); +} + /* * Return the console tty driver structure and its associated index */ |