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Commit 2f9d7389 authored by Valentin Rothberg's avatar Valentin Rothberg Committed by Jonathan Corbet
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MSI-HOWTO.txt: remove reference on IRQF_DISABLED 



The IRQF_DISABLED is a NOOP and scheduled to be removed.  According to Ingo
Molnar in commit e58aa3d2 (genirq: Run irq
handlers with interrupts disabled), 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: default avatarValentin Rothberg <Valentin.Rothberg@lip6.fr>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent 9ddfa69f

Documentation/PCI/MSI-HOWTO.txt

+3 −12
Original line number Diff line number Diff line
@@ -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