Commit f6b30d32 authored Jul 01, 2013 by James Hogan

metag: kick: add missing irq_enter/exit to kick_handler()



kick_handler() doesn't have an irq_enter/exit pair, but it's used for
handling SMP IPIs which require work to be done in softirqs, which are
invoked from irq_exit() when the hard irq nest count reaches 0.

The scheduler_ipi() callback in the IPI handler calls irq_enter/exit
itself, but this is inside kick_handler()'s spin lock critical section,
so if an invoked softirq issues an IPI the kick_handler() will be
re-entered on the same CPU and will deadlock.

This is easily fixed by adding the missing irq_enter/exit to
kick_handler() so that the hard irq nest count doesn't reach 0 until
after the spin lock has been released.

Ideally the spin lock protected handler list will also be replaced by a
lockless RCU protected list since it is certainly mostly read. That can
be done in a later change though.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

parent 96498144

arch/metag/kernel/kick.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -26,6 +26,8 @@
		* pass it as an argument.
		*/
		#include <linux/export.h>
		#include <linux/hardirq.h>
		#include <linux/irq.h>
		#include <linux/kernel.h>
		#include <linux/mm.h>
		#include <linux/types.h>
		@@ -66,6 +68,7 @@ EXPORT_SYMBOL(kick_unregister_func);
		TBIRES
		kick_handler(TBIRES State, int SigNum, int Triggers, int Inst, PTBI pTBI)
		{
		struct pt_regs *old_regs;
		struct kick_irq_handler *kh;
		struct list_head *lh;
		int handled = 0;
		@@ -79,6 +82,9 @@ kick_handler(TBIRES State, int SigNum, int Triggers, int Inst, PTBI pTBI)

		trace_hardirqs_off();

		old_regs = set_irq_regs((struct pt_regs *)State.Sig.pCtx);
		irq_enter();

		/*
		* There is no need to disable interrupts here because we
		* can't nest KICK interrupts in a KICK interrupt handler.
		@@ -97,5 +103,8 @@ kick_handler(TBIRES State, int SigNum, int Triggers, int Inst, PTBI pTBI)

		WARN_ON(!handled);

		irq_exit();
		set_irq_regs(old_regs);

		return tail_end(ret);
		}

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