The IRQF_DISABLED is a NOOP and scheduled to be removed. According to
Ingo Molnar (e58aa3d2d0cc01ad8d6f7f640a0670433f794922) running IRQ
handlers with interrupts enabled can cause stack overflows when the
interrupt line of the issuing device is still active.
This patch removes IRQF_DISABLED from this documentation. It was
mentioned to be a solution to avoid deadlocks when a device uses
multiple interrupts. As the flag is a NOOP this solution does not work
anymore.
Signed-off-by: Valentin Rothberg <[email protected]>
---
v2: Remove following paragraph (If your MSI [...]) since there is only
one solution left.
---
Documentation/PCI/MSI-HOWTO.txt | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)
diff --git a/Documentation/PCI/MSI-HOWTO.txt b/Documentation/PCI/MSI-HOWTO.txt
index 0d920d5..63def8ef 100644
--- a/Documentation/PCI/MSI-HOWTO.txt
+++ b/Documentation/PCI/MSI-HOWTO.txt
@@ -501,18 +501,9 @@ necessary to disable interrupts (Linux guarantees the same interrupt will
not be re-entered). If a device uses multiple interrupts, the driver
must disable interrupts while the lock is held. If the device sends
a different interrupt, the driver will deadlock trying to recursively
-acquire the spinlock.
-
-There are two solutions. The first is to take the lock with
-spin_lock_irqsave() or spin_lock_irq() (see
-Documentation/DocBook/kernel-locking). The second is to specify
-IRQF_DISABLED to request_irq() so that the kernel runs the entire
-interrupt routine with interrupts disabled.
-
-If your MSI interrupt routine does not hold the lock for the whole time
-it is running, the first solution may be best. The second solution is
-normally preferred as it avoids making two transitions from interrupt
-disabled to enabled and back again.
+acquire the spinlock. Such deadlocks can be avoided by using
+spin_lock_irqsave() or spin_lock_irq() which disable local interrupts
+and acquire the lock (see Documentation/DocBook/kernel-locking).
4.6 How to tell whether MSI/MSI-X is enabled on a device
--
1.9.1
On Fri, 27 Feb 2015 12:55:16 +0100
Valentin Rothberg <[email protected]> wrote:
> The IRQF_DISABLED is a NOOP and scheduled to be removed. According to
> Ingo Molnar (e58aa3d2d0cc01ad8d6f7f640a0670433f794922) running IRQ
> handlers with interrupts enabled can cause stack overflows when the
> interrupt line of the issuing device is still active.
>
> This patch removes IRQF_DISABLED from this documentation. It was
> mentioned to be a solution to avoid deadlocks when a device uses
> multiple interrupts. As the flag is a NOOP this solution does not work
> anymore.
Seems good, applied to the docs tree. I reworked the commit ID in the
changelog into the standard form (adding the one-line description),
though.
Thanks,
jon
On Fri, Feb 27, 2015 at 11:17 PM, Jonathan Corbet <[email protected]> wrote:
> On Fri, 27 Feb 2015 12:55:16 +0100
> Valentin Rothberg <[email protected]> wrote:
>
>> The IRQF_DISABLED is a NOOP and scheduled to be removed. According to
>> Ingo Molnar (e58aa3d2d0cc01ad8d6f7f640a0670433f794922) running IRQ
>> handlers with interrupts enabled can cause stack overflows when the
>> interrupt line of the issuing device is still active.
>>
>> This patch removes IRQF_DISABLED from this documentation. It was
>> mentioned to be a solution to avoid deadlocks when a device uses
>> multiple interrupts. As the flag is a NOOP this solution does not work
>> anymore.
>
> Seems good, applied to the docs tree. I reworked the commit ID in the
> changelog into the standard form (adding the one-line description),
> though.
Thank you. I will take care to add the one-line description in the future.
Valentin
> Thanks,
>
> jon