Commit 51e69e65 authored by Randy Dunlap's avatar Randy Dunlap Committed by Thomas Gleixner
Browse files

Documentation/locking/locktypes: Minor copy editor fixes 



Minor editorial fixes:
- remove 'enabled' from PREEMPT_RT enabled kernels for consistency
- add some periods for consistency
- add "'" for possessive CPU's
- spell out interrupts

[ tglx: Picked up Paul's suggestions ]

Signed-off-by: default avatarRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarPaul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/ac615f36-0b44-408d-aeab-d76e4241add4@infradead.org
parent 7ecc6aa5

Documentation/locking/locktypes.rst

+11 −11
Original line number Diff line number Diff line
@@ -84,7 +84,7 @@ rtmutex 


RT-mutexes are mutexes with support for priority inheritance (PI).



PI has limitations on non PREEMPT_RT enabled kernels due to preemption and

PI has limitations on non-PREEMPT_RT kernels due to preemption and

interrupt disabled sections.



PI clearly cannot preempt preemption-disabled or interrupt-disabled
@@ -150,7 +150,7 @@ kernel configuration including PREEMPT_RT enabled kernels. 


raw_spinlock_t is a strict spinning lock implementation in all kernels,

including PREEMPT_RT kernels.  Use raw_spinlock_t only in real critical

core code, low level interrupt handling and places where disabling

core code, low-level interrupt handling and places where disabling

preemption or interrupts is required, for example, to safely access

hardware state.  raw_spinlock_t can sometimes also be used when the

critical section is tiny, thus avoiding RT-mutex overhead.
@@ -160,20 +160,20 @@ spinlock_t 


The semantics of spinlock_t change with the state of PREEMPT_RT.



On a non PREEMPT_RT enabled kernel spinlock_t is mapped to raw_spinlock_t

and has exactly the same semantics.

On a non-PREEMPT_RT kernel spinlock_t is mapped to raw_spinlock_t and has

exactly the same semantics.



spinlock_t and PREEMPT_RT

-------------------------



On a PREEMPT_RT enabled kernel spinlock_t is mapped to a separate

implementation based on rt_mutex which changes the semantics:

On a PREEMPT_RT kernel spinlock_t is mapped to a separate implementation

based on rt_mutex which changes the semantics:



 - Preemption is not disabled

 - Preemption is not disabled.



 - The hard interrupt related suffixes for spin_lock / spin_unlock

   operations (_irq, _irqsave / _irqrestore) do not affect the CPUs

   interrupt disabled state

   operations (_irq, _irqsave / _irqrestore) do not affect the CPU's

   interrupt disabled state.



 - The soft interrupt related suffix (_bh()) still disables softirq

   handlers.
@@ -279,8 +279,8 @@ fully preemptible context. Instead, use spin_lock_irq() or 
spin_lock_irqsave() and their unlock counterparts.  In cases where the

interrupt disabling and locking must remain separate, PREEMPT_RT offers a

local_lock mechanism.  Acquiring the local_lock pins the task to a CPU,

allowing things like per-CPU irq-disabled locks to be acquired.  However,

this approach should be used only where absolutely necessary.

allowing things like per-CPU interrupt disabled locks to be acquired.

However, this approach should be used only where absolutely necessary.





raw_spinlock_t

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