Messages in this thread | | | Date | Thu, 30 Jan 2003 02:29:28 +0100 | From | Andrea Arcangeli <> | Subject | Re: frlock and barrier discussion |
| |
On Wed, Jan 29, 2003 at 05:15:55PM -0800, Stephen Hemminger wrote: > On Tue, 2003-01-28 at 23:06, Richard Henderson wrote: > > On Tue, Jan 28, 2003 at 03:42:21PM -0800, Stephen Hemminger wrote: > > > +static inline void fr_write_begin(frlock_t *rw) > > > +{ > > > + preempt_disable(); > > > + rw->pre_sequence++; > > > + wmb(); > > > +} > > > + > > > +static inline void fr_write_end(frlock_t *rw) > > > +{ > > > + wmb(); > > > + rw->post_sequence++; > > > > These need to be mb(), not wmb(), if you want the bits in between > > to actually happen in between, as with your xtime example. At > > present there's nothing stoping xtime from being *read* before > > your read from pre_sequence happens. > > > First, write_begin/end can only be safely used when there is separate > writer synchronization such as a spin_lock or semaphore. > As far as I know, semaphore or spin_lock guarantees a barrier. > So xtime or anything else can not be read before the spin_lock. > > Using mb() is more paranoid than necessary.
yes, it should only generate a superflous lock on x86.
it shouldn't even be necessary in fr_write_trylock.
Andrea - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |