[PATCH V2] arm64: traps: disable irq in die()

[PATCH V2] arm64: traps: disable irq in die()

[Qiao Zhou]

In current die(), the irq is disabled for __die() handle, not
including the possible panic() handling. Since the log in __die()
can take several hundreds ms, new irq might come and interrupt
current die().

If the process calling die() holds some critical resource, and some
other process scheduled later also needs it, then it would deadlock.
The first panic will not be executed.

So here disable irq for the whole flow of die().

Signed-off-by: Qiao Zhou <qiaozhou@asrmicro.com>
---
 arch/arm64/kernel/traps.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index 0805b44..2e2ff88 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -274,10 +274,12 @@ static DEFINE_RAW_SPINLOCK(die_lock);
 void die(const char *str, struct pt_regs *regs, int err)
 {
 	int ret;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&die_lock, flags);
 
 	oops_enter();
 
-	raw_spin_lock_irq(&die_lock);
 	console_verbose();
 	bust_spinlocks(1);
 	ret = __die(str, err, regs);
@@ -287,13 +289,15 @@ void die(const char *str, struct pt_regs *regs, int err)
 
 	bust_spinlocks(0);
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
-	raw_spin_unlock_irq(&die_lock);
 	oops_exit();
 
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
 	if (panic_on_oops)
 		panic("Fatal exception");
+
+	raw_spin_unlock_irqrestore(&die_lock, flags);
+
 	if (ret != NOTIFY_STOP)
 		do_exit(SIGSEGV);
 }
-- 
2.7.4

[PATCH V2] arm64: traps: disable irq in die()

[Zhou Qiao(周侨)]

Hi Maintainers,

Could you please help to take a look and give some comments? Thanks in advance.

Best Regards
Qiao

-----Original Message-----
From: Zhou Qiao
Sent: Friday, July 07, 2017 5:30 PM
To: catalin.marinas at arm.com; will.deacon at arm.com; mark.rutland at arm.com; suzuki.poulose at arm.com; mingo at kernel.org; marc.zyngier at arm.com; andre.przywara at arm.com; linux-arm-kernel at lists.infradead.org; linux-kernel at vger.kernel.org
Cc: Zhou Qiao
Subject: [PATCH V2] arm64: traps: disable irq in die()

In current die(), the irq is disabled for __die() handle, not including the possible panic() handling. Since the log in __die() can take several hundreds ms, new irq might come and interrupt current die().

If the process calling die() holds some critical resource, and some other process scheduled later also needs it, then it would deadlock.
The first panic will not be executed.

So here disable irq for the whole flow of die().

Signed-off-by: Qiao Zhou <qiaozhou@asrmicro.com>
---
 arch/arm64/kernel/traps.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c index 0805b44..2e2ff88 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -274,10 +274,12 @@ static DEFINE_RAW_SPINLOCK(die_lock);  void die(const char *str, struct pt_regs *regs, int err)  {
 	int ret;
+	unsigned long flags;
+
+	raw_spin_lock_irqsave(&die_lock, flags);
 
 	oops_enter();
 
-	raw_spin_lock_irq(&die_lock);
 	console_verbose();
 	bust_spinlocks(1);
 	ret = __die(str, err, regs);
@@ -287,13 +289,15 @@ void die(const char *str, struct pt_regs *regs, int err)
 
 	bust_spinlocks(0);
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
-	raw_spin_unlock_irq(&die_lock);
 	oops_exit();
 
 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
 	if (panic_on_oops)
 		panic("Fatal exception");
+
+	raw_spin_unlock_irqrestore(&die_lock, flags);
+
 	if (ret != NOTIFY_STOP)
 		do_exit(SIGSEGV);
 }
--
2.7.4

[PATCH V2] arm64: traps: disable irq in die()

[Will Deacon]

On Fri, Jul 21, 2017 at 07:38:42AM +0000, Zhou Qiao(??) wrote:
> Could you please help to take a look and give some comments? Thanks in
> advance.

I've queued this on the arm64 for-next/fixes/core branch.

Will

[PATCH V2] arm64: traps: disable irq in die()

[qiaozhou]

On 2017?07?21? 16:32, Will Deacon wrote:
> On Fri, Jul 21, 2017 at 07:38:42AM +0000, Zhou Qiao(??) wrote:
>> Could you please help to take a look and give some comments? Thanks in
>> advance.
> I've queued this on the arm64 for-next/fixes/core branch.
Got it. Thanks!
>
> Will
Best Regards
Qiao