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[Qemu-devel] [PULL 11/39] atomic.h: comment on use of atomic_read/set
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 11/39] atomic.h: comment on use of atomic_read/set |
Date: |
Fri, 7 Oct 2016 18:57:35 +0200 |
From: Alex Bennée <address@hidden>
Add some notes on the use of the relaxed atomic access helpers and their
importance for defined behaviour in C11's multi-threaded memory model.
Signed-off-by: Alex Bennée <address@hidden>
Message-Id: <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
---
include/qemu/atomic.h | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h
index c493f89..c4f6950 100644
--- a/include/qemu/atomic.h
+++ b/include/qemu/atomic.h
@@ -92,6 +92,12 @@
/* Weak atomic operations prevent the compiler moving other
* loads/stores past the atomic operation load/store. However there is
* no explicit memory barrier for the processor.
+ *
+ * The C11 memory model says that variables that are accessed from
+ * different threads should at least be done with __ATOMIC_RELAXED
+ * primitives or the result is undefined. Generally this has little to
+ * no effect on the generated code but not using the atomic primitives
+ * will get flagged by sanitizers as a violation.
*/
#define atomic_read(ptr) \
({ \
--
2.7.4
- [Qemu-devel] [PULL 02/39] MC146818 RTC: coordinate guest clock base to destination host after migration, (continued)
- [Qemu-devel] [PULL 02/39] MC146818 RTC: coordinate guest clock base to destination host after migration, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 01/39] hw/iommu: Fix problems reported by Coverity scan, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 03/39] hw/misc/edu: support MSI interrupt, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 04/39] intc: add an interface to gather statistics/informations on interrupt controllers, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 05/39] intc/i8259: implement InterruptStatsProvider interface, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 06/39] intc/slavio_intctl: implement InterruptStatsProvider interface, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 07/39] intc/lm32_pic: implement InterruptStatsProvider interface, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 08/39] intc: make HMP 'info irq' and 'info pic' commands use InterruptStatsProvider interface, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 09/39] intc: make HMP 'info irq' and 'info pic' commands available on all targets, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 10/39] atomic.h: fix __SANITIZE_THREAD__ build, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 11/39] atomic.h: comment on use of atomic_read/set,
Paolo Bonzini <=
- [Qemu-devel] [PULL 12/39] tcg/optimize: move default return out of if statement, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 13/39] seqlock: use atomic writes for the sequence, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 14/39] qom/object: update class cache atomically, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 15/39] qom/cpu: atomically clear the tb_jmp_cache, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 16/39] cpu: atomically modify cpu->exit_request, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 17/39] util/qht: atomically set b->hashes, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 18/39] linux-user/syscall: extend lock around cpu-list, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 19/39] qga/command: use QEMU atomic primitives, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 20/39] .travis.yml: add gcc sanitizer build, Paolo Bonzini, 2016/10/07
- [Qemu-devel] [PULL 22/39] char: use a fixed idx for child muxed chr, Paolo Bonzini, 2016/10/07