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authorValentin Rothberg <Valentin.Rothberg@lip6.fr>2015-02-27 12:55:16 +0100
committerJonathan Corbet <corbet@lwn.net>2015-03-20 07:41:55 -0600
commit2f9d7389b5e243abd0c42995a703c4f7cf535af4 (patch)
treeceae1b6569ea4af8cbba5196f4900ed968b852ab
parent9ddfa69fb073081882505a4f69d3f0c344d9bcaf (diff)
downloadop-kernel-dev-2f9d7389b5e243abd0c42995a703c4f7cf535af4.zip
op-kernel-dev-2f9d7389b5e243abd0c42995a703c4f7cf535af4.tar.gz
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 e58aa3d2d0cc01ad8d6f7f640a0670433f794922 (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: Valentin Rothberg <Valentin.Rothberg@lip6.fr> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
-rw-r--r--Documentation/PCI/MSI-HOWTO.txt15
1 files 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
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