| Message ID | 1493226006-7600-1-git-send-email-odpbot@yandex.ru |
|---|---|
| State | New |
| Headers | show |
That does not work. Since the value of cnt is not checked, the code would happily take the lock even when a writer already has it. Janne > -----Original Message----- > From: lng-odp [mailto:lng-odp-bounces@lists.linaro.org] On Behalf Of Github ODP bot > Sent: Wednesday, April 26, 2017 8:00 PM > To: lng-odp@lists.linaro.org > Subject: [lng-odp] [PATCH] linux-generic: rwlock: fix odp_rwlock_read_trylock() > > From: Dmitry Eremin-Solenikov <dmitry.ereminsolenikov@linaro.org> > > odp_rwlock_read_trylock() currently works only if there are no readers > (and writers) as it compares counter with 0. Make it actually work in > case there are other active readers. > > Fixes: https://bugs.linaro.org/show_bug.cgi?id=2974 > > Signed-off-by: Dmitry Eremin-Solenikov <dmitry.ereminsolenikov@linaro.org> > --- > /** Email created from pull request 19 (lumag:fix-rwlock) > ** https://github.com/Linaro/odp/pull/19 > ** Patch: https://github.com/Linaro/odp/pull/19.patch > ** Base sha: 9b993a1531c94782b48292adff54a95de9d2be5c > ** Merge commit sha: 3af3b11b695d157ce1649955b52e8a165cc82937 > **/ > platform/linux-generic/odp_rwlock.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/platform/linux-generic/odp_rwlock.c b/platform/linux-generic/odp_rwlock.c > index 13c17a2..e0c46ce 100644 > --- a/platform/linux-generic/odp_rwlock.c > +++ b/platform/linux-generic/odp_rwlock.c > @@ -33,9 +33,9 @@ void odp_rwlock_read_lock(odp_rwlock_t *rwlock) > > int odp_rwlock_read_trylock(odp_rwlock_t *rwlock) > { > - uint32_t zero = 0; > + uint32_t cnt = odp_atomic_load_u32(&rwlock->cnt); > > - return odp_atomic_cas_acq_u32(&rwlock->cnt, &zero, (uint32_t)1); > + return odp_atomic_cas_acq_u32(&rwlock->cnt, &cnt, cnt + 1); > } > > void odp_rwlock_read_unlock(odp_rwlock_t *rwlock)
On 26.04.2017 20:54, Peltonen, Janne (Nokia - FI/Espoo) wrote: > > That does not work. Since the value of cnt is not checked, the code > would happily take the lock even when a writer already has it. Nice catch. Updated to check for writers. -- With best wishes Dmitry
diff --git a/platform/linux-generic/odp_rwlock.c b/platform/linux-generic/odp_rwlock.c index 13c17a2..e0c46ce 100644 --- a/platform/linux-generic/odp_rwlock.c +++ b/platform/linux-generic/odp_rwlock.c @@ -33,9 +33,9 @@ void odp_rwlock_read_lock(odp_rwlock_t *rwlock) int odp_rwlock_read_trylock(odp_rwlock_t *rwlock) { - uint32_t zero = 0; + uint32_t cnt = odp_atomic_load_u32(&rwlock->cnt); - return odp_atomic_cas_acq_u32(&rwlock->cnt, &zero, (uint32_t)1); + return odp_atomic_cas_acq_u32(&rwlock->cnt, &cnt, cnt + 1); } void odp_rwlock_read_unlock(odp_rwlock_t *rwlock)