linux-kernel - [PATCH 3.16 21/63] arm64: traps: disable irq in die()

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Date:   Wed, 08 Jan 2020 19:43:19 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Qiao Zhou" <qiaozhou@...micro.com>,
        "Will Deacon" <will.deacon@....com>
Subject: [PATCH 3.16 21/63] arm64: traps: disable irq in die()

3.16.81-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Qiao Zhou <qiaozhou@...micro.com>

commit 6f44a0bacb79a03972c83759711832b382b1b8ac upstream.

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@...micro.com>
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/arm64/kernel/traps.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -178,10 +178,12 @@ void die(const char *str, struct pt_regs
 {
 	struct thread_info *thread = current_thread_info();
 	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, thread, regs);
@@ -191,13 +193,15 @@ void die(const char *str, struct pt_regs
 
 	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);
 }