This is a note to let you know that I've just added the patch titled
irqchip: armada-370-xp: fix IPI race condition
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
irqchip-armada-370-xp-fix-ipi-race-condition.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a6f089e95b1e08cdea9633d50ad20aa5d44ba64d Mon Sep 17 00:00:00 2001
From: Lior Amsalem <alior@xxxxxxxxxxx>
Date: Mon, 25 Nov 2013 17:26:44 +0100
Subject: irqchip: armada-370-xp: fix IPI race condition
From: Lior Amsalem <alior@xxxxxxxxxxx>
commit a6f089e95b1e08cdea9633d50ad20aa5d44ba64d upstream.
In the Armada 370/XP driver, when we receive an IRQ 0, we read the
list of doorbells that caused the interrupt from register
ARMADA_370_XP_IN_DRBEL_CAUSE_OFFS. This gives the list of IPIs that
were generated. However, instead of acknowledging only the IPIs that
were generated, we acknowledge *all* the IPIs, by writing
~IPI_DOORBELL_MASK in the ARMADA_370_XP_IN_DRBEL_CAUSE_OFFS register.
This creates a race condition: if a new IPI that isn't part of the
ones read into the temporary "ipimask" variable is fired before we
acknowledge all IPIs, then we will simply loose it. This is causing
scheduling hangs on SMP intensive workloads.
It is important to mention that this ARMADA_370_XP_IN_DRBEL_CAUSE_OFFS
register has the following behavior: "A CPU write of 0 clears the bits
in this field. A CPU write of 1 has no effect". This is what allows us
to simply write ~ipimask to acknoledge the handled IPIs.
Notice that the same problem is present in the MSI implementation, but
it will be fixed as a separate patch, so that this IPI fix can be
pushed to older stable versions as appropriate (all the way to 3.8),
while the MSI code only appeared in 3.13.
Signed-off-by: Lior Amsalem <alior@xxxxxxxxxxx>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
Fixes: 344e873e5657e8dc0 'arm: mvebu: Add IPI support via doorbells'
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Jason Cooper <jason@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/irqchip/irq-armada-370-xp.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/irqchip/irq-armada-370-xp.c
+++ b/drivers/irqchip/irq-armada-370-xp.c
@@ -229,7 +229,7 @@ armada_370_xp_handle_irq(struct pt_regs
ARMADA_370_XP_IN_DRBEL_CAUSE_OFFS)
& IPI_DOORBELL_MASK;
- writel(~IPI_DOORBELL_MASK, per_cpu_int_base +
+ writel(~ipimask, per_cpu_int_base +
ARMADA_370_XP_IN_DRBEL_CAUSE_OFFS);
/* Handle all pending doorbells */
Patches currently in stable-queue which might be from alior@xxxxxxxxxxx are
queue-3.12/irqchip-armada-370-xp-fix-ipi-race-condition.patch
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