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| author | Richard Henderson <rth@redhat.com> | 2014-02-20 09:43:53 -0800 |
|---|---|---|
| committer | Richard Henderson <rth@gcc.gnu.org> | 2014-02-20 09:43:53 -0800 |
| commit | 672ce9397b78c077e21d785a2ddf9fffd51a1952 (patch) | |
| tree | 8ec4b08823b9b5486cecde9c93f376b7f59cf42e /libatomic | |
| parent | 95ce7613d537f5a3e9e36da0ca6aa752f60da8e0 (diff) | |
| download | gcc-672ce9397b78c077e21d785a2ddf9fffd51a1952.zip gcc-672ce9397b78c077e21d785a2ddf9fffd51a1952.tar.gz gcc-672ce9397b78c077e21d785a2ddf9fffd51a1952.tar.bz2 | |
re PR c++/60272 (atomic<>::compare_exchange_weak has spurious store and can cause race conditions)
PR c++/60272
gcc/
* builtins.c (expand_builtin_atomic_compare_exchange): Conditionalize
on failure the store back into EXPECT.
libatomic/
* cas_n.c (libat_compare_exchange): Conditionalize on failure
the store back to EPTR.
From-SVN: r207966
Diffstat (limited to 'libatomic')
| -rw-r--r-- | libatomic/ChangeLog | 6 | ||||
| -rw-r--r-- | libatomic/cas_n.c | 25 |
2 files changed, 18 insertions, 13 deletions
diff --git a/libatomic/ChangeLog b/libatomic/ChangeLog index 2d1c9bd..1bd3c21 100644 --- a/libatomic/ChangeLog +++ b/libatomic/ChangeLog @@ -1,3 +1,9 @@ +2014-02-20 Richard Henderson <rth@redhat.com> + + PR c++/60272 + * cas_n.c (libat_compare_exchange): Conditionalize on failure + the store back to EPTR. + 2014-01-02 Richard Sandiford <rdsandiford@googlemail.com> Update copyright years diff --git a/libatomic/cas_n.c b/libatomic/cas_n.c index 39c7833..801262d 100644 --- a/libatomic/cas_n.c +++ b/libatomic/cas_n.c @@ -51,10 +51,9 @@ SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, #if !DONE && N <= WORDSIZE && defined(atomic_compare_exchange_w) bool SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, - int smodel, int fmodel UNUSED) + int smodel, int fmodel) { UWORD mask, shift, weval, woldval, wnewval, t, *wptr; - bool ret = false; pre_barrier (smodel); @@ -82,12 +81,13 @@ SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, } while (!atomic_compare_exchange_w (wptr, &woldval, t, true, __ATOMIC_RELAXED, __ATOMIC_RELAXED)); - ret = true; + post_barrier (smodel); + return true; + failure: *eptr = woldval >> shift; - - post_barrier (smodel); - return ret; + post_barrier (fmodel); + return false; } #define DONE 1 @@ -102,18 +102,17 @@ SIZE(libat_compare_exchange) (UTYPE *mptr, UTYPE *eptr, UTYPE newval, { UTYPE oldval; UWORD magic; - bool ret = false; + bool ret; pre_seq_barrier (smodel); magic = protect_start (mptr); oldval = *mptr; - if (oldval == *eptr) - { - *mptr = newval; - ret = true; - } - *eptr = oldval; + ret = (oldval == *eptr); + if (ret) + *mptr = newval; + else + *eptr = oldval; protect_end (mptr, magic); post_seq_barrier (smodel); |