From 47b8f3ab9c49daa824af848f9e02889662d8638f Mon Sep 17 00:00:00 2001 From: Elena Reshetova Date: Wed, 30 Jan 2019 13:18:51 +0200 Subject: 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) Signed-off-by: Elena Reshetova Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Andrea Parri Cc: Andrew Morton Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon 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 --- lib/refcount.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) (limited to 'lib/refcount.c') 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 @@ -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 */ -- cgit