Re: [BUG]: when printk too more through serial, cpu up is failed.
On Fri, Mar 15, 2013 at 09:26:26AM +0800, Shuge wrote:
> 于 2013年03月14日 22:05, Greg KH 写道:
> >On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
> >>Hi all,
> >> When the kernel printk too many log, the cpu is failed to come online.
> >>The problem is this:
> >>For example, cpu0 bring up cpu1:
> >>
> >> a. cpu0 call cpu_up:
> >> cpu_up()
> >> ->_cpu_up()
> >> ->__cpu_notify(CPU_UP_PREPARE)
> >> ->__cpu_up()
> >>->boot_secondary()
> >># ->wait_for_completion_timeout(_running, msecs_to_jiffires(1000))
> >> -> if (!cpu_online(cpu)) {
> >> pr_crit("CPU%u: failed to come online\n", cpu);
> >> ret = -EIO;
> >> }
> >> ->cpu_notify(CPU_ONLINE)
> >>
> >> b. cpu1 enter kernel:
> >> secondary_start_kernel()
> >>@ ->printk("CPU%u: Booted secondary processor\n", cpu)
> >>* ->calibrate_delay()
> >> ->set_cpu_online()
> >> ->complete(cpu_running)
> >> ->cpumask_set_cpu()
> >>
> >>While cpu0 run to mark #, which wait that cpu1 complete
> >>cpu_running, and set online.
> >>Generally, cpu0 can get it. But if the __log_buf is too large or
> >>other threads write
> >>it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
> >>busy outputing
> >>buffer, which cost time more than 1s, and cpu1 have not join in
> >>sched, so cpu0 wait it timeout.
> >>By reading printk.c, I found that can_use_console() always return
> >>true, which be called by
> >>console_trylock_for_printk(). Because, have_callable_console()
> >>return ture always, if the console
> >>driver set CON_ANYTIME flag. I think that cpu should not output the
> >>__log_buf in coming online,
> >>even though have_callable_console() is true.
> >>
> >>/*
> >> * Can we actually use the console at this time on this cpu?
> >> *
> >> * Console drivers may assume that per-cpu resources have
> >> * been allocated. So unless they're explicitly marked as
> >> * being able to cope (CON_ANYTIME) don't call them until
> >> * this CPU is officially up.
> >> */
> >>static inline int can_use_console(unsigned int cpu)
> >>{
> >> return cpu_online(cpu) || have_callable_console();
> >>}
> >>
> >>In can_use_console, why not is &&, but ||?
> >>
> >>Kernel Version: 3.3.0
> >Why such an old and obsolete kernel version? Please try this on 3.8,
> >lots of work have gone into the printk area that should have solved this
> >issue.
> >
> >greg k-h
>
> I saw the printk.c in version 3.9, it still check
> console_trylock_for_printk() to decide to call console_unlock. In
> vprintk_emit(), cpu1 also have the opportunity to execute
> console_unlock() at coming online time.
> Once cpu which is coming online can output buffer, nothing can
> interrupt it until buffer is empty.But we can't ensure that none
> always write the __log_buf. It is danger!
Do you really hit this with a real system? Is your cpu just really slow
in initializing? What is the actual time it takes?
> I think, the solution is that we should prevent to use console at
> coming online.
Ok, what would be your proposed patch to solve this?
greg k-h
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Re: [BUG]: when printk too more through serial, cpu up is failed.
On Fri, Mar 15, 2013 at 09:26:26AM +0800, Shuge wrote:
于 2013年03月14日 22:05, Greg KH 写道:
On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
-_cpu_up()
-__cpu_notify(CPU_UP_PREPARE)
-__cpu_up()
-boot_secondary()
# -wait_for_completion_timeout(cpu_running, msecs_to_jiffires(1000))
- if (!cpu_online(cpu)) {
pr_crit(CPU%u: failed to come online\n, cpu);
ret = -EIO;
}
-cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ -printk(CPU%u: Booted secondary processor\n, cpu)
* -calibrate_delay()
-set_cpu_online()
-complete(cpu_running)
-cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or
other threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
busy outputing
buffer, which cost time more than 1s, and cpu1 have not join in
sched, so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console()
return ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is , but ||?
Kernel Version: 3.3.0
Why such an old and obsolete kernel version? Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.
greg k-h
I saw the printk.c in version 3.9, it still check
console_trylock_for_printk() to decide to call console_unlock. In
vprintk_emit(), cpu1 also have the opportunity to execute
console_unlock() at coming online time.
Once cpu which is coming online can output buffer, nothing can
interrupt it until buffer is empty.But we can't ensure that none
always write the __log_buf. It is danger!
Do you really hit this with a real system? Is your cpu just really slow
in initializing? What is the actual time it takes?
I think, the solution is that we should prevent to use console at
coming online.
Ok, what would be your proposed patch to solve this?
greg k-h
--
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the body of a message to majord...@vger.kernel.org
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Please read the FAQ at http://www.tux.org/lkml/
Re: [BUG]: when printk too more through serial, cpu up is failed.
于 2013年03月14日 22:05, Greg KH 写道:
On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
->_cpu_up()
->__cpu_notify(CPU_UP_PREPARE)
->__cpu_up()
->boot_secondary()
# ->wait_for_completion_timeout(_running, msecs_to_jiffires(1000))
-> if (!cpu_online(cpu)) {
pr_crit("CPU%u: failed to come online\n", cpu);
ret = -EIO;
}
->cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ ->printk("CPU%u: Booted secondary processor\n", cpu)
* ->calibrate_delay()
->set_cpu_online()
->complete(cpu_running)
->cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or
other threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
busy outputing
buffer, which cost time more than 1s, and cpu1 have not join in
sched, so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console()
return ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is &&, but ||?
Kernel Version: 3.3.0
Why such an old and obsolete kernel version? Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.
greg k-h
I saw the printk.c in version 3.9, it still check
console_trylock_for_printk() to decide to call console_unlock. In
vprintk_emit(), cpu1 also have the opportunity to execute
console_unlock() at coming online time.
Once cpu which is coming online can output buffer, nothing can interrupt
it until buffer is empty.But we can't ensure that none always write the
__log_buf. It is danger! I think, the solution is that we should prevent
to use console at coming online.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [BUG]: when printk too more through serial, cpu up is failed.
On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
> Hi all,
> When the kernel printk too many log, the cpu is failed to come online.
> The problem is this:
> For example, cpu0 bring up cpu1:
>
> a. cpu0 call cpu_up:
> cpu_up()
> ->_cpu_up()
> ->__cpu_notify(CPU_UP_PREPARE)
> ->__cpu_up()
>->boot_secondary()
> # ->wait_for_completion_timeout(_running, msecs_to_jiffires(1000))
> -> if (!cpu_online(cpu)) {
> pr_crit("CPU%u: failed to come online\n", cpu);
> ret = -EIO;
> }
> ->cpu_notify(CPU_ONLINE)
>
> b. cpu1 enter kernel:
> secondary_start_kernel()
> @ ->printk("CPU%u: Booted secondary processor\n", cpu)
> * ->calibrate_delay()
> ->set_cpu_online()
> ->complete(cpu_running)
> ->cpumask_set_cpu()
>
>While cpu0 run to mark #, which wait that cpu1 complete
> cpu_running, and set online.
> Generally, cpu0 can get it. But if the __log_buf is too large or
> other threads write
> it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
> busy outputing
> buffer, which cost time more than 1s, and cpu1 have not join in
> sched, so cpu0 wait it timeout.
>By reading printk.c, I found that can_use_console() always return
> true, which be called by
> console_trylock_for_printk(). Because, have_callable_console()
> return ture always, if the console
> driver set CON_ANYTIME flag. I think that cpu should not output the
> __log_buf in coming online,
> even though have_callable_console() is true.
>
> /*
> * Can we actually use the console at this time on this cpu?
> *
> * Console drivers may assume that per-cpu resources have
> * been allocated. So unless they're explicitly marked as
> * being able to cope (CON_ANYTIME) don't call them until
> * this CPU is officially up.
> */
> static inline int can_use_console(unsigned int cpu)
> {
> return cpu_online(cpu) || have_callable_console();
> }
>
> In can_use_console, why not is &&, but ||?
>
> Kernel Version: 3.3.0
Why such an old and obsolete kernel version? Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.
greg k-h
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[BUG]: when printk too more through serial, cpu up is failed.
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
->_cpu_up()
->__cpu_notify(CPU_UP_PREPARE)
->__cpu_up()
->boot_secondary()
# ->wait_for_completion_timeout(_running, msecs_to_jiffires(1000))
-> if (!cpu_online(cpu)) {
pr_crit("CPU%u: failed to come online\n", cpu);
ret = -EIO;
}
->cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ ->printk("CPU%u: Booted secondary processor\n", cpu)
* ->calibrate_delay()
->set_cpu_online()
->complete(cpu_running)
->cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or other
threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is busy
outputing
buffer, which cost time more than 1s, and cpu1 have not join in sched,
so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console() return
ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is &&, but ||?
Kernel Version: 3.3.0
Arch: arm
This problem trace:
[ 1722.150286] CPU1: Booted secondary processor
[ 1722.154613] Calibrating delay loop (skipped) already calibrated this CPU
.
[ 1725.134687] CPU1: failed to come online
.
[ 1728.055547] [ cut here ]
[ 1728.060219] kernel BUG at kernel/workqueue.c:3332!
[ 1728.065010] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 1728.070503] Modules linked in: cdc_ether rtl8150 mcs7830 qf9700 asix
usbnet mma7660 sw_keyboard gt9xx g2d_33 sunxi_csi1 gc2035 ov5640
videobuf_dma_contig videobuf_core dc_sunxi(O) pvrsrvkm(O) nand(O)
[ 1728.088474] CPU: 0Tainted: G O (3.3.0 #9)
[ 1728.093796] PC is at trustee_thread+0x24/0x514
[ 1728.098239] LR is at trustee_thread+0x1c/0x514
[ 1728.102683] pc : []lr : []psr: 2013
[ 1728.102690] sp : ec05bf68 ip : ec05bf68 fp : ec05bfb4
[ 1728.114161] r10: r9 : r8 :
[ 1728.119383] r7 : 0013 r6 : c059c72c r5 : 0001 r4 : e5e162c0
[ 1728.125906] r3 : r2 : 0001 r1 : ec05bf40 r0 :
[ 1728.132432] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM
Segment kernel
[ 1728.139736] Control: 10c53c7d Table: 6e35c06a DAC: 0015
.
[ 1728.709566] Process workqueue_trust (pid: 22196, stack limit =
0xec05a2f8)
[ 1728.716436] Stack: (0xec05bf68 to 0xec05c000)
[ 1728.720796] bf60: c05a6c3c c007f98c c07ed100
c07ed100 c05a788c ed089de0
[ 1728.728973] bf80: e5e162c0 c059c72c 0013 ed089de0 e5e162c0
c059c72c 0013
[ 1728.737148] bfa0: ec05bff4 ec05bfb8 c00732fc
c059c738
[ 1728.745324] bfc0: e5e162c0 ec05bfd0
ec05bfd0 ed089de0
[ 1728.753501] bfe0: c0073260 c0057d50 ec05bff8 c0057d50
c007326c 00d851b1 da280100
[ 1728.761669] Backtrace:
[ 1728.764140] [] (trustee_thread+0x0/0x514) from []
(kthread+0x9c/0xa8)
[ 1728.772321] [] (kthread+0x0/0xa8) from []
(do_exit+0x0/0x764)
[ 1728.779797] r6:c0057d50 r5:c0073260 r4:ed089de0
[ 1728.784457] Code: e1a04000 ebf36dbd e155 0a00 (e7f001f2)
[ 1729.130494] ---[ end trace 3deba094f67f9e11 ]---
[ 1729.140018] Kernel panic - not syncing: Fatal exception
[ 1730.355119] SMP: failed to stop secondary CPUs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[BUG]: when printk too more through serial, cpu up is failed.
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
-_cpu_up()
-__cpu_notify(CPU_UP_PREPARE)
-__cpu_up()
-boot_secondary()
# -wait_for_completion_timeout(cpu_running, msecs_to_jiffires(1000))
- if (!cpu_online(cpu)) {
pr_crit(CPU%u: failed to come online\n, cpu);
ret = -EIO;
}
-cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ -printk(CPU%u: Booted secondary processor\n, cpu)
* -calibrate_delay()
-set_cpu_online()
-complete(cpu_running)
-cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or other
threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is busy
outputing
buffer, which cost time more than 1s, and cpu1 have not join in sched,
so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console() return
ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is , but ||?
Kernel Version: 3.3.0
Arch: arm
This problem trace:
[ 1722.150286] CPU1: Booted secondary processor
[ 1722.154613] Calibrating delay loop (skipped) already calibrated this CPU
.
[ 1725.134687] CPU1: failed to come online
.
[ 1728.055547] [ cut here ]
[ 1728.060219] kernel BUG at kernel/workqueue.c:3332!
[ 1728.065010] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP
[ 1728.070503] Modules linked in: cdc_ether rtl8150 mcs7830 qf9700 asix
usbnet mma7660 sw_keyboard gt9xx g2d_33 sunxi_csi1 gc2035 ov5640
videobuf_dma_contig videobuf_core dc_sunxi(O) pvrsrvkm(O) nand(O)
[ 1728.088474] CPU: 0Tainted: G O (3.3.0 #9)
[ 1728.093796] PC is at trustee_thread+0x24/0x514
[ 1728.098239] LR is at trustee_thread+0x1c/0x514
[ 1728.102683] pc : [c059c750]lr : [c059c748]psr: 2013
[ 1728.102690] sp : ec05bf68 ip : ec05bf68 fp : ec05bfb4
[ 1728.114161] r10: r9 : r8 :
[ 1728.119383] r7 : 0013 r6 : c059c72c r5 : 0001 r4 : e5e162c0
[ 1728.125906] r3 : r2 : 0001 r1 : ec05bf40 r0 :
[ 1728.132432] Flags: nzCv IRQs on FIQs on Mode SVC_32 ISA ARM
Segment kernel
[ 1728.139736] Control: 10c53c7d Table: 6e35c06a DAC: 0015
.
[ 1728.709566] Process workqueue_trust (pid: 22196, stack limit =
0xec05a2f8)
[ 1728.716436] Stack: (0xec05bf68 to 0xec05c000)
[ 1728.720796] bf60: c05a6c3c c007f98c c07ed100
c07ed100 c05a788c ed089de0
[ 1728.728973] bf80: e5e162c0 c059c72c 0013 ed089de0 e5e162c0
c059c72c 0013
[ 1728.737148] bfa0: ec05bff4 ec05bfb8 c00732fc
c059c738
[ 1728.745324] bfc0: e5e162c0 ec05bfd0
ec05bfd0 ed089de0
[ 1728.753501] bfe0: c0073260 c0057d50 ec05bff8 c0057d50
c007326c 00d851b1 da280100
[ 1728.761669] Backtrace:
[ 1728.764140] [c059c72c] (trustee_thread+0x0/0x514) from [c00732fc]
(kthread+0x9c/0xa8)
[ 1728.772321] [c0073260] (kthread+0x0/0xa8) from [c0057d50]
(do_exit+0x0/0x764)
[ 1728.779797] r6:c0057d50 r5:c0073260 r4:ed089de0
[ 1728.784457] Code: e1a04000 ebf36dbd e155 0a00 (e7f001f2)
[ 1729.130494] ---[ end trace 3deba094f67f9e11 ]---
[ 1729.140018] Kernel panic - not syncing: Fatal exception
[ 1730.355119] SMP: failed to stop secondary CPUs
--
To unsubscribe from this list: send the line unsubscribe linux-kernel in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Re: [BUG]: when printk too more through serial, cpu up is failed.
On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
-_cpu_up()
-__cpu_notify(CPU_UP_PREPARE)
-__cpu_up()
-boot_secondary()
# -wait_for_completion_timeout(cpu_running, msecs_to_jiffires(1000))
- if (!cpu_online(cpu)) {
pr_crit(CPU%u: failed to come online\n, cpu);
ret = -EIO;
}
-cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ -printk(CPU%u: Booted secondary processor\n, cpu)
* -calibrate_delay()
-set_cpu_online()
-complete(cpu_running)
-cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or
other threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
busy outputing
buffer, which cost time more than 1s, and cpu1 have not join in
sched, so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console()
return ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is , but ||?
Kernel Version: 3.3.0
Why such an old and obsolete kernel version? Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.
greg k-h
--
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Re: [BUG]: when printk too more through serial, cpu up is failed.
于 2013年03月14日 22:05, Greg KH 写道:
On Thu, Mar 14, 2013 at 09:51:34PM +0800, Shuge wrote:
Hi all,
When the kernel printk too many log, the cpu is failed to come online.
The problem is this:
For example, cpu0 bring up cpu1:
a. cpu0 call cpu_up:
cpu_up()
-_cpu_up()
-__cpu_notify(CPU_UP_PREPARE)
-__cpu_up()
-boot_secondary()
# -wait_for_completion_timeout(cpu_running, msecs_to_jiffires(1000))
- if (!cpu_online(cpu)) {
pr_crit(CPU%u: failed to come online\n, cpu);
ret = -EIO;
}
-cpu_notify(CPU_ONLINE)
b. cpu1 enter kernel:
secondary_start_kernel()
@ -printk(CPU%u: Booted secondary processor\n, cpu)
* -calibrate_delay()
-set_cpu_online()
-complete(cpu_running)
-cpumask_set_cpu()
While cpu0 run to mark #, which wait that cpu1 complete
cpu_running, and set online.
Generally, cpu0 can get it. But if the __log_buf is too large or
other threads write
it unceasing, then cpu1 come to mark @ or * in this moment. Cpu1 is
busy outputing
buffer, which cost time more than 1s, and cpu1 have not join in
sched, so cpu0 wait it timeout.
By reading printk.c, I found that can_use_console() always return
true, which be called by
console_trylock_for_printk(). Because, have_callable_console()
return ture always, if the console
driver set CON_ANYTIME flag. I think that cpu should not output the
__log_buf in coming online,
even though have_callable_console() is true.
/*
* Can we actually use the console at this time on this cpu?
*
* Console drivers may assume that per-cpu resources have
* been allocated. So unless they're explicitly marked as
* being able to cope (CON_ANYTIME) don't call them until
* this CPU is officially up.
*/
static inline int can_use_console(unsigned int cpu)
{
return cpu_online(cpu) || have_callable_console();
}
In can_use_console, why not is , but ||?
Kernel Version: 3.3.0
Why such an old and obsolete kernel version? Please try this on 3.8,
lots of work have gone into the printk area that should have solved this
issue.
greg k-h
I saw the printk.c in version 3.9, it still check
console_trylock_for_printk() to decide to call console_unlock. In
vprintk_emit(), cpu1 also have the opportunity to execute
console_unlock() at coming online time.
Once cpu which is coming online can output buffer, nothing can interrupt
it until buffer is empty.But we can't ensure that none always write the
__log_buf. It is danger! I think, the solution is that we should prevent
to use console at coming online.
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