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| author |   Andrew Murray <andrew.murray@arm.com> | 2018-10-08 14:15:15 +0100 |
|---|---|---|
| committer |   Jonathan Corbet <corbet@lwn.net> | 2018-10-12 11:35:47 -0600 |
| commit | 44280690ced5dacd3004d4966ef9b15f940f34e0 (patch) | |
| tree | 8d4a42b829b48e74be0301ebf9fcf1c761a9a066 /Documentation/preempt-locking.txt | |
| parent | dm flakey: Document "error_writes" feature (diff) | |
| download | linux-dev-44280690ced5dacd3004d4966ef9b15f940f34e0.tar.xz linux-dev-44280690ced5dacd3004d4966ef9b15f940f34e0.zip | |
Documentation: preempt-locking: Use better example
The existing wording implies that the use of spin_unlock whilst irqs are
disabled might trigger a reschedule. However the preemptible() test in
preempt_schedule will prevent a reschedule if irqs are disabled.
Lets improve the clarity of this wording to change the example from
spin_unlock to cond_resched() and cond_resched_lock() as these are
functions that will trigger a reschedule if the preempt count is 0 without
testing that irqs are disabled.
Also remove the 'Last Updated' line as this is not up to date and better
tracked via GIT.
Signed-off-by: Andrew Murray <andrew.murray@arm.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Diffstat (limited to 'Documentation/preempt-locking.txt')
| -rw-r--r-- | Documentation/preempt-locking.txt | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/Documentation/preempt-locking.txt b/Documentation/preempt-locking.txt index c945062be66c..509f5a422d57 100644 --- a/Documentation/preempt-locking.txt +++ b/Documentation/preempt-locking.txt @@ -3,7 +3,6 @@ Proper Locking Under a Preemptible Kernel: Keeping Kernel Code Preempt-Safe =========================================================================== :Author: Robert Love <rml@tech9.net> -:Last Updated: 28 Aug 2002 Introduction @@ -92,11 +91,12 @@ any locks or interrupts are disabled, since preemption is implicitly disabled in those cases. But keep in mind that 'irqs disabled' is a fundamentally unsafe way of -disabling preemption - any spin_unlock() decreasing the preemption count -to 0 might trigger a reschedule. A simple printk() might trigger a reschedule. -So use this implicit preemption-disabling property only if you know that the -affected codepath does not do any of this. Best policy is to use this only for -small, atomic code that you wrote and which calls no complex functions. +disabling preemption - any cond_resched() or cond_resched_lock() might trigger +a reschedule if the preempt count is 0. A simple printk() might trigger a +reschedule. So use this implicit preemption-disabling property only if you +know that the affected codepath does not do any of this. Best policy is to use +this only for small, atomic code that you wrote and which calls no complex +functions. Example:: |