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author | Elena Reshetova <elena.reshetova@intel.com> | 2019-01-30 13:18:51 +0200 |
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committer | Ingo Molnar <mingo@kernel.org> | 2019-02-04 09:03:31 +0100 |
commit | 47b8f3ab9c49daa824af848f9e02889662d8638f (patch) | |
tree | bd42ab897748eafaacdc5d0bb97256a678cee3d5 /lib | |
parent | 412f34a82ccf7dd52f6b197f6450a33f03342523 (diff) | |
download | linux-47b8f3ab9c49daa824af848f9e02889662d8638f.tar.gz linux-47b8f3ab9c49daa824af848f9e02889662d8638f.tar.bz2 linux-47b8f3ab9c49daa824af848f9e02889662d8638f.zip |
refcount_t: Add ACQUIRE ordering on success for dec(sub)_and_test() variants
This adds an smp_acquire__after_ctrl_dep() barrier on successful
decrease of refcounter value from 1 to 0 for refcount_dec(sub)_and_test
variants and therefore gives stronger memory ordering guarantees than
prior versions of these functions.
Co-developed-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Cc: dvyukov@google.com
Cc: keescook@chromium.org
Cc: stern@rowland.harvard.edu
Link: https://lkml.kernel.org/r/1548847131-27854-2-git-send-email-elena.reshetova@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/refcount.c | 18 |
1 files changed, 13 insertions, 5 deletions
diff --git a/lib/refcount.c b/lib/refcount.c index ebcf8cd49e05..6e904af0fb3e 100644 --- a/lib/refcount.c +++ b/lib/refcount.c @@ -33,6 +33,9 @@ * Note that the allocator is responsible for ordering things between free() * and alloc(). * + * The decrements dec_and_test() and sub_and_test() also provide acquire + * ordering on success. + * */ #include <linux/mutex.h> @@ -164,8 +167,8 @@ EXPORT_SYMBOL(refcount_inc_checked); * at UINT_MAX. * * Provides release memory ordering, such that prior loads and stores are done - * before, and provides a control dependency such that free() must come after. - * See the comment on top. + * before, and provides an acquire ordering on success such that free() + * must come after. * * Use of this function is not recommended for the normal reference counting * use case in which references are taken and released one at a time. In these @@ -190,7 +193,12 @@ bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r) } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); - return !new; + if (!new) { + smp_acquire__after_ctrl_dep(); + return true; + } + return false; + } EXPORT_SYMBOL(refcount_sub_and_test_checked); @@ -202,8 +210,8 @@ EXPORT_SYMBOL(refcount_sub_and_test_checked); * decrement when saturated at UINT_MAX. * * Provides release memory ordering, such that prior loads and stores are done - * before, and provides a control dependency such that free() must come after. - * See the comment on top. + * before, and provides an acquire ordering on success such that free() + * must come after. * * Return: true if the resulting refcount is 0, false otherwise */ |