Hello, I feel I don't really like this patch but I am travelling without my working laptop, can't read the source code ;) Quite possibly I am wrong, I'll return to this when I get back on May 10.
Oleg. On 05/07, Uladzislau Rezki (Sony) wrote: > > From: "Paul E. McKenney" <[email protected]> > > The rcu_sync structure's ->gp_count field is updated under the protection > of ->rss_lock, but read locklessly, and KCSAN noted the data race. > This commit therefore uses WRITE_ONCE() to do this update to clearly > document its racy nature. > > Signed-off-by: Paul E. McKenney <[email protected]> > Cc: Oleg Nesterov <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Signed-off-by: Uladzislau Rezki (Sony) <[email protected]> > --- > kernel/rcu/sync.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c > index 86df878a2fee..6c2bd9001adc 100644 > --- a/kernel/rcu/sync.c > +++ b/kernel/rcu/sync.c > @@ -122,7 +122,7 @@ void rcu_sync_enter(struct rcu_sync *rsp) > * we are called at early boot time but this shouldn't happen. > */ > } > - rsp->gp_count++; > + WRITE_ONCE(rsp->gp_count, rsp->gp_count + 1); > spin_unlock_irq(&rsp->rss_lock); > > if (gp_state == GP_IDLE) { > @@ -151,11 +151,15 @@ void rcu_sync_enter(struct rcu_sync *rsp) > */ > void rcu_sync_exit(struct rcu_sync *rsp) > { > + int gpc; > + > WARN_ON_ONCE(READ_ONCE(rsp->gp_state) == GP_IDLE); > WARN_ON_ONCE(READ_ONCE(rsp->gp_count) == 0); > > spin_lock_irq(&rsp->rss_lock); > - if (!--rsp->gp_count) { > + gpc = rsp->gp_count - 1; > + WRITE_ONCE(rsp->gp_count, gpc); > + if (!gpc) { > if (rsp->gp_state == GP_PASSED) { > WRITE_ONCE(rsp->gp_state, GP_EXIT); > rcu_sync_call(rsp); > -- > 2.39.2 >
