Ralf Baechle 写道:
On Thu, Mar 04, 2010 at 10:23:47AM -0800, David Daney wrote:
On 03/04/2010 01:39 AM, Yang Shi wrote:
During machine restart with reboot command, get the following
bug info:
BUG: using smp_processor_id() in preemptible [00000000] code: reboot/1989
caller is __udelay+0x14/0x70
Call Trace:
[<ffffffff8110ad28>] dump_stack+0x8/0x34
[<ffffffff812dde04>] debug_smp_processor_id+0xf4/0x110
[<ffffffff812d90bc>] __udelay+0x14/0x70
[<ffffffff81378274>] md_notify_reboot+0x12c/0x148
[<ffffffff81161054>] notifier_call_chain+0x64/0xc8
[<ffffffff811614dc>] __blocking_notifier_call_chain+0x64/0xc0
[<ffffffff8115566c>] kernel_restart_prepare+0x1c/0x38
[<ffffffff811556cc>] kernel_restart+0x14/0x50
[<ffffffff8115581c>] SyS_reboot+0x10c/0x1f0
[<ffffffff81103684>] handle_sysn32+0x44/0x84
The root cause is that current_cpu_data is accessed in preemptible
context, so protect it with preempt_disable/preempt_enable pair
in delay().
Signed-off-by: Yang Shi<yang.shi@xxxxxxxxxxxxx>
---
arch/mips/lib/delay.c | 6 +++++-
1 files changed, 5 insertions(+), 1 deletions(-)
diff --git a/arch/mips/lib/delay.c b/arch/mips/lib/delay.c
index 6b3b1de..dc38064 100644
--- a/arch/mips/lib/delay.c
+++ b/arch/mips/lib/delay.c
@@ -41,7 +41,11 @@ EXPORT_SYMBOL(__delay);
void __udelay(unsigned long us)
{
- unsigned int lpj = current_cpu_data.udelay_val;
+ unsigned int lpj;
+
+ preempt_disable();
+ lpj = current_cpu_data.udelay_val;
+ preempt_enable();
__delay((us * 0x000010c7ull * HZ * lpj)>> 32);
}
This doesn't seem like the best approach.
Perhaps we should either use raw_current_cpu_data and no
preempt_disable(), or if we are concerned about migrating to a CPU
with a different lpj value, move the preempt_enable after the call
to __delay().
Udelay() is supposed to guarantee a minimum delay and when being migrated
to another CPU with higher bogomips this guarantee might be violated. So
it'd even have to be something like:
void __udelay(unsigned long us)
{
unsigned int lpj = current_cpu_data.udelay_val;
unsigned int lpj;
preempt_disable();
lpj = current_cpu_data.udelay_val;
__delay((us * 0x000010c7ull * HZ * lpj)>> 32);
preempt_enable();
}
But preempt_disable() itself is not atomic, so using it from bh or irq
context could result in a corrupted preemption counter. So the raw_
version will have to do. I doubt it's much of a problem but at some
point we will have to revisit the delay by c0_count patch submitted a
while ago. The patch wasn't right but the problem it was addressing
is real.
Thanks Ralf. Do we need raw_ version patch before revisiting the delay
by c0_count patch although it's not an ideal fix.
Regards,
Yang
Ralf
