From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> To: kbuild test robot <lkp@intel.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, kbuild-all@01.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>, Daniel Wang <wonderfly@google.com>, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Alan Cox <gnomes@lxorguk.ukuu.org.uk>, Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>, linux-serial@vger.kernel.org, Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Subject: Re: [PATCHv3] panic: avoid deadlocks in re-entrant console drivers Date: Thu, 25 Oct 2018 20:56:15 +0900 [thread overview] Message-ID: <20181025115615.GA1018@tigerII.localdomain> (raw) In-Reply-To: <201810251848.0wSJMnS0%fengguang.wu@intel.com> On (10/25/18 18:51), kbuild test robot wrote: > > [auto build test ERROR on linux-sof-driver/master] > [also build test ERROR on v4.19 next-20181019] > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] > My bad, sorry! +#include <linux/vt_kern.h> This should fix it. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Subject: [PATCH] panic: avoid deadlocks in re-entrant console drivers From printk()/serial console point of view panic() is special, because it may force CPU to re-enter printk() or/and serial console driver. Therefore, some of serial consoles drivers are re-entrant. E.g. 8250: serial8250_console_write() { if (port->sysrq) locked = 0; else if (oops_in_progress) locked = spin_trylock_irqsave(&port->lock, flags); else spin_lock_irqsave(&port->lock, flags); ... } panic() does set oops_in_progress via bust_spinlocks(1), so in theory we should be able to re-enter serial console driver from panic(): CPU0 <NMI> uart_console_write() serial8250_console_write() // if (oops_in_progress) // spin_trylock_irqsave() call_console_drivers() console_unlock() console_flush_on_panic() bust_spinlocks(1) // oops_in_progress++ panic() <NMI/> spin_lock_irqsave(&port->lock, flags) // spin_lock_irqsave() serial8250_console_write() call_console_drivers() console_unlock() printk() ... However, this does not happen and we deadlock in serial console on port->lock spinlock. And the problem is that console_flush_on_panic() called after bust_spinlocks(0): void panic(const char *fmt, ...) { bust_spinlocks(1); ... bust_spinlocks(0); console_flush_on_panic(); ... } bust_spinlocks(0) decrements oops_in_progress, so oops_in_progress can go back to zero. Thus even re-entrant console drivers will simply spin on port->lock spinlock. Given that port->lock may already be locked either by a stopped CPU, or by the very same CPU we execute panic() on (for instance, NMI panic() on printing CPU) the system deadlocks and does not reboot. Fix this by removing bust_spinlocks(0), so oops_in_progress is always set in panic() now and, thus, re-entrant console drivers will trylock the port->lock instead of spinning on it forever, when we call them from console_flush_on_panic(). Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- kernel/panic.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/panic.c b/kernel/panic.c index f6d549a29a5c..272ac1c34e4b 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -29,6 +29,7 @@ #include <linux/ratelimit.h> #include <linux/debugfs.h> #include <asm/sections.h> +#include <linux/vt_kern.h> #define PANIC_TIMER_STEP 100 #define PANIC_BLINK_SPD 18 @@ -237,7 +238,10 @@ void panic(const char *fmt, ...) if (_crash_kexec_post_notifiers) __crash_kexec(NULL); - bust_spinlocks(0); +#ifdef CONFIG_VT + unblank_screen(); +#endif + console_unblank(); /* * We may have ended up stopping the CPU holding the lock (in -- 2.19.1
WARNING: multiple messages have this Message-ID (diff)
From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> To: kbuild test robot <lkp@intel.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, kbuild-all@01.org, linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>, Steven Rostedt <rostedt@goodmis.org>, Daniel Wang <wonderfly@google.com>, Peter Zijlstra <peterz@infradead.org>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Alan Cox <gnomes@lxorguk.ukuu.org.uk>, Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>, linux-serial@vger.kernel.org, Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Subject: Re: [PATCHv3] panic: avoid deadlocks in re-entrant console drivers Date: Thu, 25 Oct 2018 20:56:15 +0900 [thread overview] Message-ID: <20181025115615.GA1018@tigerII.localdomain> (raw) In-Reply-To: <201810251848.0wSJMnS0%fengguang.wu@intel.com> On (10/25/18 18:51), kbuild test robot wrote: > > [auto build test ERROR on linux-sof-driver/master] > [also build test ERROR on v4.19 next-20181019] > [if your patch is applied to the wrong git tree, please drop us a note to help improve the system] > My bad, sorry! +#include <linux/vt_kern.h> This should fix it. =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> Subject: [PATCH] panic: avoid deadlocks in re-entrant console drivers >From printk()/serial console point of view panic() is special, because it may force CPU to re-enter printk() or/and serial console driver. Therefore, some of serial consoles drivers are re-entrant. E.g. 8250: serial8250_console_write() { if (port->sysrq) locked = 0; else if (oops_in_progress) locked = spin_trylock_irqsave(&port->lock, flags); else spin_lock_irqsave(&port->lock, flags); ... } panic() does set oops_in_progress via bust_spinlocks(1), so in theory we should be able to re-enter serial console driver from panic(): CPU0 <NMI> uart_console_write() serial8250_console_write() // if (oops_in_progress) // spin_trylock_irqsave() call_console_drivers() console_unlock() console_flush_on_panic() bust_spinlocks(1) // oops_in_progress++ panic() <NMI/> spin_lock_irqsave(&port->lock, flags) // spin_lock_irqsave() serial8250_console_write() call_console_drivers() console_unlock() printk() ... However, this does not happen and we deadlock in serial console on port->lock spinlock. And the problem is that console_flush_on_panic() called after bust_spinlocks(0): void panic(const char *fmt, ...) { bust_spinlocks(1); ... bust_spinlocks(0); console_flush_on_panic(); ... } bust_spinlocks(0) decrements oops_in_progress, so oops_in_progress can go back to zero. Thus even re-entrant console drivers will simply spin on port->lock spinlock. Given that port->lock may already be locked either by a stopped CPU, or by the very same CPU we execute panic() on (for instance, NMI panic() on printing CPU) the system deadlocks and does not reboot. Fix this by removing bust_spinlocks(0), so oops_in_progress is always set in panic() now and, thus, re-entrant console drivers will trylock the port->lock instead of spinning on it forever, when we call them from console_flush_on_panic(). Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> --- kernel/panic.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/kernel/panic.c b/kernel/panic.c index f6d549a29a5c..272ac1c34e4b 100644 --- a/kernel/panic.c +++ b/kernel/panic.c @@ -29,6 +29,7 @@ #include <linux/ratelimit.h> #include <linux/debugfs.h> #include <asm/sections.h> +#include <linux/vt_kern.h> #define PANIC_TIMER_STEP 100 #define PANIC_BLINK_SPD 18 @@ -237,7 +238,10 @@ void panic(const char *fmt, ...) if (_crash_kexec_post_notifiers) __crash_kexec(NULL); - bust_spinlocks(0); +#ifdef CONFIG_VT + unblank_screen(); +#endif + console_unblank(); /* * We may have ended up stopping the CPU holding the lock (in -- 2.19.1
next prev parent reply other threads:[~2018-10-25 11:56 UTC|newest] Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-10-16 5:04 [RFC][PATCHv2 0/4] less deadlock prone serial consoles Sergey Senozhatsky 2018-10-16 5:04 ` [RFC][PATCHv2 1/4] panic: avoid deadlocks in re-entrant console drivers Sergey Senozhatsky 2018-10-16 5:04 ` Sergey Senozhatsky 2018-10-17 4:48 ` Sergey Senozhatsky 2018-10-23 11:07 ` Petr Mladek 2018-10-23 11:54 ` Sergey Senozhatsky 2018-10-23 12:04 ` Sergey Senozhatsky 2018-10-23 12:12 ` Sergey Senozhatsky 2018-10-25 9:06 ` Petr Mladek 2018-10-25 9:31 ` Sergey Senozhatsky 2018-10-25 8:29 ` Petr Mladek 2018-10-25 9:05 ` Sergey Senozhatsky 2018-10-25 10:10 ` [PATCHv3] " Sergey Senozhatsky 2018-10-25 10:10 ` Sergey Senozhatsky 2018-10-25 10:51 ` kbuild test robot 2018-10-25 10:51 ` kbuild test robot 2018-10-25 11:56 ` Sergey Senozhatsky [this message] 2018-10-25 11:56 ` Sergey Senozhatsky 2018-10-31 12:27 ` Petr Mladek 2018-11-01 1:48 ` Sergey Senozhatsky 2018-11-01 8:08 ` Petr Mladek 2018-11-22 13:12 ` Petr Mladek 2018-12-12 0:53 ` Daniel Wang 2018-12-12 5:23 ` Sergey Senozhatsky 2018-12-12 5:59 ` Daniel Wang 2018-12-12 6:06 ` Sergey Senozhatsky 2018-12-12 6:09 ` Daniel Wang 2018-10-16 5:04 ` [RFC][PATCHv2 2/4] printk: move printk_safe macros to printk header Sergey Senozhatsky 2018-10-16 7:27 ` Peter Zijlstra 2018-10-16 11:40 ` Petr Mladek 2018-10-16 12:17 ` Peter Zijlstra 2018-10-17 10:50 ` Petr Mladek 2018-10-17 14:00 ` Peter Zijlstra 2018-10-22 14:30 ` Petr Mladek 2018-10-16 12:27 ` Sergey Senozhatsky 2018-10-16 12:38 ` Peter Zijlstra 2018-10-16 12:54 ` Peter Zijlstra 2018-10-16 14:21 ` Peter Zijlstra 2018-10-17 4:32 ` Sergey Senozhatsky 2018-10-17 4:32 ` Sergey Senozhatsky 2018-10-17 7:57 ` Peter Zijlstra 2018-10-17 13:36 ` Sergey Senozhatsky 2018-10-23 6:25 ` Sergey Senozhatsky 2018-10-16 5:04 ` [RFC][PATCHv2 3/4] serial: introduce uart_port locking helpers Sergey Senozhatsky 2018-12-08 3:12 ` Sergey Senozhatsky 2018-12-12 11:08 ` Greg Kroah-Hartman 2018-10-16 5:04 ` [RFC][PATCHv2 4/4] tty: 8250: switch to " Sergey Senozhatsky 2018-10-16 7:23 ` [RFC][PATCHv2 0/4] less deadlock prone serial consoles Peter Zijlstra 2018-10-16 8:12 ` Sergey Senozhatsky
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