* Re: [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization
2012-09-03 15:34 [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization Paolo Bonzini
@ 2012-09-03 15:43 ` Jan Kiszka
2012-09-03 15:45 ` Aurelien Jarno
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Jan Kiszka @ 2012-09-03 15:43 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: aliguori, qemu-devel, aurelien
On 2012-09-03 17:34, Paolo Bonzini wrote:
> QEMU will hang when fed the following command-line
>
> qemu-system-mips -kernel vmlinux-2.6.32-5-4kc-malta -append "console=ttyS0" -nographic -net none
>
> The -net none is important otherwise it seems some events are generated
> causing the things to work. When it doesn't work, the guest hangs when
> measuring the CPU frequency, after the following line:
>
> [ 0.000000] NR_IRQS:256
>
> Pressing a key on the serial port unblocks it, hinting that the problem
> is due to the recent elimination of the 1 second timeout in the main
> loop.
>
> The problem is that because init_timer_alarm sets the timer's pending
> flag to true, the alarm timer is never armed until after the first time
> through the main loop. Thus the bug started when QEMU started testing
> the pending flag in qemu_mod_timer (commit 1828be3, more alarm timer
> cleanup, 2010-03-10).
>
> But actually, it isn't true at all that a timer is pending when the
> alarm timer is created, and the real bug has been latent forever: the
> fix is to remove the bogus setting of pending flag.
>
> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> qemu-timer.c | 3 ---
> 1 file modificato, 3 rimozioni(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 5aea94e..c7a1551 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -759,11 +759,8 @@ int init_timer_alarm(void)
> goto fail;
> }
>
> - /* first event is at time 0 */
> atexit(quit_timers);
> - t->pending = true;
> alarm_timer = t;
> -
> return 0;
>
> fail:
>
Funnily, I just create the same problem with my "run timer handlers in
signal handler" patch (*). Same solution there.
Reviewed-by: Jan Kiszka <jan.kiszka@siemens.com>
Jan
(*) I will go for select-based timers once I have time for the necessary
refactorings.
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization
2012-09-03 15:34 [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization Paolo Bonzini
2012-09-03 15:43 ` Jan Kiszka
@ 2012-09-03 15:45 ` Aurelien Jarno
2012-09-04 7:06 ` Michael Tokarev
2012-09-04 10:32 ` Aurelien Jarno
3 siblings, 0 replies; 5+ messages in thread
From: Aurelien Jarno @ 2012-09-03 15:45 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: aliguori, qemu-devel
On Mon, Sep 03, 2012 at 05:34:32PM +0200, Paolo Bonzini wrote:
> QEMU will hang when fed the following command-line
>
> qemu-system-mips -kernel vmlinux-2.6.32-5-4kc-malta -append "console=ttyS0" -nographic -net none
>
> The -net none is important otherwise it seems some events are generated
> causing the things to work. When it doesn't work, the guest hangs when
> measuring the CPU frequency, after the following line:
>
> [ 0.000000] NR_IRQS:256
>
> Pressing a key on the serial port unblocks it, hinting that the problem
> is due to the recent elimination of the 1 second timeout in the main
> loop.
>
> The problem is that because init_timer_alarm sets the timer's pending
> flag to true, the alarm timer is never armed until after the first time
> through the main loop. Thus the bug started when QEMU started testing
> the pending flag in qemu_mod_timer (commit 1828be3, more alarm timer
> cleanup, 2010-03-10).
>
> But actually, it isn't true at all that a timer is pending when the
> alarm timer is created, and the real bug has been latent forever: the
> fix is to remove the bogus setting of pending flag.
>
> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> qemu-timer.c | 3 ---
> 1 file modificato, 3 rimozioni(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 5aea94e..c7a1551 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -759,11 +759,8 @@ int init_timer_alarm(void)
> goto fail;
> }
>
> - /* first event is at time 0 */
> atexit(quit_timers);
> - t->pending = true;
> alarm_timer = t;
> -
> return 0;
>
> fail:
>
Thanks a lot that was quite fast!
Tested-by: Aurelien Jarno <aurelien@aurel32.net>
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien@aurel32.net http://www.aurel32.net
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization
2012-09-03 15:34 [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization Paolo Bonzini
2012-09-03 15:43 ` Jan Kiszka
2012-09-03 15:45 ` Aurelien Jarno
@ 2012-09-04 7:06 ` Michael Tokarev
2012-09-04 10:32 ` Aurelien Jarno
3 siblings, 0 replies; 5+ messages in thread
From: Michael Tokarev @ 2012-09-04 7:06 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: aliguori, qemu-devel, aurelien, Qemu-stable@nongnu.org
On 03.09.2012 19:34, Paolo Bonzini wrote:
> QEMU will hang when fed the following command-line
>
> qemu-system-mips -kernel vmlinux-2.6.32-5-4kc-malta -append "console=ttyS0" -nographic -net none
>
> The -net none is important otherwise it seems some events are generated
> causing the things to work. When it doesn't work, the guest hangs when
> measuring the CPU frequency, after the following line:
>
> [ 0.000000] NR_IRQS:256
>
> Pressing a key on the serial port unblocks it, hinting that the problem
> is due to the recent elimination of the 1 second timeout in the main
> loop.
>
> The problem is that because init_timer_alarm sets the timer's pending
> flag to true, the alarm timer is never armed until after the first time
> through the main loop. Thus the bug started when QEMU started testing
> the pending flag in qemu_mod_timer (commit 1828be3, more alarm timer
> cleanup, 2010-03-10).
>
> But actually, it isn't true at all that a timer is pending when the
> alarm timer is created, and the real bug has been latent forever: the
> fix is to remove the bogus setting of pending flag.
>
> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> qemu-timer.c | 3 ---
> 1 file modificato, 3 rimozioni(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 5aea94e..c7a1551 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -759,11 +759,8 @@ int init_timer_alarm(void)
> goto fail;
> }
>
> - /* first event is at time 0 */
> atexit(quit_timers);
> - t->pending = true;
> alarm_timer = t;
> -
> return 0;
>
> fail:
This also fixes the pty-char hang I reported yesterday
in thread "apparently missing yet another notify_event()".
Tested-By: Michael Tokarev <mjt@tls.msk.ru>
This should go to 1.1-stable too, as this problem exists
there, with both -net none and -serial pty being reproducers.
Cc'ing -stable.
Thanks!
/mjt
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization
2012-09-03 15:34 [Qemu-devel] [PATCH for 1.2] qemu-timer: properly arm alarm timer for timers set by device initialization Paolo Bonzini
` (2 preceding siblings ...)
2012-09-04 7:06 ` Michael Tokarev
@ 2012-09-04 10:32 ` Aurelien Jarno
3 siblings, 0 replies; 5+ messages in thread
From: Aurelien Jarno @ 2012-09-04 10:32 UTC (permalink / raw)
To: Paolo Bonzini; +Cc: aliguori, qemu-devel
On Mon, Sep 03, 2012 at 05:34:32PM +0200, Paolo Bonzini wrote:
> QEMU will hang when fed the following command-line
>
> qemu-system-mips -kernel vmlinux-2.6.32-5-4kc-malta -append "console=ttyS0" -nographic -net none
>
> The -net none is important otherwise it seems some events are generated
> causing the things to work. When it doesn't work, the guest hangs when
> measuring the CPU frequency, after the following line:
>
> [ 0.000000] NR_IRQS:256
>
> Pressing a key on the serial port unblocks it, hinting that the problem
> is due to the recent elimination of the 1 second timeout in the main
> loop.
>
> The problem is that because init_timer_alarm sets the timer's pending
> flag to true, the alarm timer is never armed until after the first time
> through the main loop. Thus the bug started when QEMU started testing
> the pending flag in qemu_mod_timer (commit 1828be3, more alarm timer
> cleanup, 2010-03-10).
>
> But actually, it isn't true at all that a timer is pending when the
> alarm timer is created, and the real bug has been latent forever: the
> fix is to remove the bogus setting of pending flag.
>
> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
> qemu-timer.c | 3 ---
> 1 file modificato, 3 rimozioni(-)
>
> diff --git a/qemu-timer.c b/qemu-timer.c
> index 5aea94e..c7a1551 100644
> --- a/qemu-timer.c
> +++ b/qemu-timer.c
> @@ -759,11 +759,8 @@ int init_timer_alarm(void)
> goto fail;
> }
>
> - /* first event is at time 0 */
> atexit(quit_timers);
> - t->pending = true;
> alarm_timer = t;
> -
> return 0;
>
> fail:
Thanks, I have applied it.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
aurelien@aurel32.net http://www.aurel32.net
^ permalink raw reply [flat|nested] 5+ messages in thread