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authorLinus Torvalds <torvalds@linux-foundation.org>2018-06-05 02:40:11 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2018-06-05 02:40:11 +0300
commit92400b8c8b42e53abb0fcb4ac75cb85d4177a891 (patch)
treeb6c7ef758d1c2b5e32e2483a0dbde7cd23a6d8a0 /Documentation/core-api
parent31a85cb35c82d686a95f903fdf9a346aba818290 (diff)
parent1b22fc609cecd1b16c4a015e1a6b3c9717484e3a (diff)
downloadlinux-92400b8c8b42e53abb0fcb4ac75cb85d4177a891.tar.xz
Merge branch 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking updates from Ingo Molnar: - Lots of tidying up changes all across the map for Linux's formal memory/locking-model tooling, by Alan Stern, Akira Yokosawa, Andrea Parri, Paul E. McKenney and SeongJae Park. Notable changes beyond an overall update in the tooling itself is the tidying up of spin_is_locked() semantics, which spills over into the kernel proper as well. - qspinlock improvements: the locking algorithm now guarantees forward progress whereas the previous implementation in mainline could starve threads indefinitely in cmpxchg() loops. Also other related cleanups to the qspinlock code (Will Deacon) - misc smaller improvements, cleanups and fixes all across the locking subsystem * 'locking-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits) locking/rwsem: Simplify the is-owner-spinnable checks tools/memory-model: Add reference for 'Simplifying ARM concurrency' tools/memory-model: Update ASPLOS information MAINTAINERS, tools/memory-model: Update e-mail address for Andrea Parri tools/memory-model: Fix coding style in 'lock.cat' tools/memory-model: Remove out-of-date comments and code from lock.cat tools/memory-model: Improve mixed-access checking in lock.cat tools/memory-model: Improve comments in lock.cat tools/memory-model: Remove duplicated code from lock.cat tools/memory-model: Flag "cumulativity" and "propagation" tests tools/memory-model: Add model support for spin_is_locked() tools/memory-model: Add scripts to test memory model tools/memory-model: Fix coding style in 'linux-kernel.def' tools/memory-model: Model 'smp_store_mb()' tools/memory-order: Update the cheat-sheet to show that smp_mb__after_atomic() orders later RMW operations tools/memory-order: Improve key for SELF and SV tools/memory-model: Fix cheat sheet typo tools/memory-model: Update required version of herdtools7 tools/memory-model: Redefine rb in terms of rcu-fence tools/memory-model: Rename link and rcu-path to rcu-link and rb ...
Diffstat (limited to 'Documentation/core-api')
-rw-r--r--Documentation/core-api/atomic_ops.rst13
1 files changed, 7 insertions, 6 deletions
diff --git a/Documentation/core-api/atomic_ops.rst b/Documentation/core-api/atomic_ops.rst
index fce929144ccd..2e7165f86f55 100644
--- a/Documentation/core-api/atomic_ops.rst
+++ b/Documentation/core-api/atomic_ops.rst
@@ -111,7 +111,6 @@ If the compiler can prove that do_something() does not store to the
variable a, then the compiler is within its rights transforming this to
the following::
- tmp = a;
if (a > 0)
for (;;)
do_something();
@@ -119,7 +118,7 @@ the following::
If you don't want the compiler to do this (and you probably don't), then
you should use something like the following::
- while (READ_ONCE(a) < 0)
+ while (READ_ONCE(a) > 0)
do_something();
Alternatively, you could place a barrier() call in the loop.
@@ -467,10 +466,12 @@ Like the above, except that these routines return a boolean which
indicates whether the changed bit was set _BEFORE_ the atomic bit
operation.
-WARNING! It is incredibly important that the value be a boolean,
-ie. "0" or "1". Do not try to be fancy and save a few instructions by
-declaring the above to return "long" and just returning something like
-"old_val & mask" because that will not work.
+
+.. warning::
+ It is incredibly important that the value be a boolean, ie. "0" or "1".
+ Do not try to be fancy and save a few instructions by declaring the
+ above to return "long" and just returning something like "old_val &
+ mask" because that will not work.
For one thing, this return value gets truncated to int in many code
paths using these interfaces, so on 64-bit if the bit is set in the