FAILED: patch "[PATCH] printk: do cond_resched() between lines while outputting to" failed to apply to 4.3-stable tree
Subsystems (3)
[email protected]
maintainerThe patch below does not apply to the 4.3-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
Quoted 1 line
From
8d91f8b15361dfb438ab6eb3b319e2ded43458ffMon Sep 17 00:00:00 2001
From: Tejun Heo <[email protected]>
Date: Fri, 15 Jan 2016 16:58:24 -0800
Subject: [PATCH] printk: do cond_resched() between lines while outputting to
consoles
@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.
include/linux/console.h +1 -0
@@ -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 *);
kernel/panic.c +1 -2
@@ -180,8 +180,7 @@ 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;
kernel/printk/printk.c +34 -1
@@ -2234,13 +2234,24 @@ 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 */
@@ -2312,6 +2323,9 @@ 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 ;
@@ -2379,6 +2393,25 @@ 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 */