Commit ff3da2e0 authored Apr 02, 2008 by Benjamin Herrenschmidt Committed by Paul Mackerras Apr 03, 2008

[POWERPC] Fix iSeries hard irq enabling regression



A subtle bug sneaked into iSeries recently.  On this platform, we must
not normally clear MSR:EE (the hardware external interrupt enable)
except for short periods of time.  Taking an interrupt while
soft-disabled doesn't cause us to clear it for example.

The iSeries kernel expects to mostly run with MSR:EE enabled at all
times except in a few exception entry/exit code paths.  Thus
local_irq_enable() doesn't check if it needs to hard-enable as it
expects this to be unnecessary on iSeries.

However, hard_irq_disable() _does_ cause MSR:EE to be cleared,
including on iSeries.  A call to it was recently added to the
context switch code, thus causing interrupts to become disabled
for a long periods of time, causing the iSeries watchdog to kick
in under some circumstances and other nasty things.

This patch fixes it by making local_irq_enable() properly re-enable
MSR:EE on iSeries.  It basically removes a return statement here
to make iSeries use the same code path as everybody else.  That does
mean that we might occasionally get spurious decrementer interrupts
but I don't think that matters.

Another option would have been to make hard_irq_disable() a nop
on iSeries but I didn't like it much, in case we have good reasons
to hard-disable.

Part of the patch is fixes to make sure the hard_enabled PACA field
is properly set on iSeries as it used not to be before, since it
was mostly unused.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

parent 025306f3

arch/powerpc/kernel/head_64.S

+7 −6

Original line number	Diff line number	Diff line
		@@ -1387,12 +1387,14 @@ __secondary_start:
		#ifdef CONFIG_PPC_ISERIES
		BEGIN_FW_FTR_SECTION
		ori r4,r4,MSR_EE
		li r8,1
		stb r8,PACAHARDIRQEN(r13)
		END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
		#endif
		BEGIN_FW_FTR_SECTION
		stb r7,PACASOFTIRQEN(r13)
		stb r7,PACAHARDIRQEN(r13)
		END_FW_FTR_SECTION_IFCLR(FW_FEATURE_ISERIES)
		stb r7,PACASOFTIRQEN(r13)

		mtspr SPRN_SRR0,r3
		mtspr SPRN_SRR1,r4
		@@ -1520,13 +1522,12 @@ _INIT_GLOBAL(start_here_common)
		#ifdef CONFIG_PPC_ISERIES
		BEGIN_FW_FTR_SECTION
		mfmsr r5
		ori r5,r5,MSR_EE /* Hard Enabled */
		ori r5,r5,MSR_EE /* Hard Enabled on iSeries*/
		mtmsrd r5
		li r5,1
		END_FW_FTR_SECTION_IFSET(FW_FEATURE_ISERIES)
		#endif
		BEGIN_FW_FTR_SECTION
		stb r5,PACAHARDIRQEN(r13)
		END_FW_FTR_SECTION_IFCLR(FW_FEATURE_ISERIES)
		stb r5,PACAHARDIRQEN(r13) /* Hard Disabled on others */

		bl .start_kernel

arch/powerpc/kernel/irq.c

+0 −1

Original line number	Diff line number	Diff line
		@@ -143,7 +143,6 @@ void local_irq_restore(unsigned long en)
		*/
		if (local_paca->lppaca_ptr->int_dword.any_int)
		iseries_handle_interrupts();
		return;
		}

		/*