Kosuke Tatsukawa <tatsu@xxxxxxxxxxxxx> writes: > There are several places in net/sunrpc/svcsock.c which calls > waitqueue_active() without calling a memory barrier. Add a memory > barrier just as in wq_has_sleeper(). > > I found this issue when I was looking through the linux source code > for places calling waitqueue_active() before wake_up*(), but without > preceding memory barriers, after sending a patch to fix a similar > issue in drivers/tty/n_tty.c (Details about the original issue can be > found here: https://lkml.org/lkml/2015/9/28/849). hi, this feels like the wrong approach to the problem. It requires extra 'smb_mb's to be spread around which are hard to understand as easy to forget. A quick look seems to suggest that (nearly) every waitqueue_active() will need an smb_mb. Could we just put the smb_mb() inside waitqueue_active()?? Thanks, NeilBrown > > Signed-off-by: Kosuke Tatsukawa <tatsu@xxxxxxxxxxxxx> > --- > v2: > - Fixed compiler warnings caused by type mismatch > v1: > - https://lkml.org/lkml/2015/10/8/993 > --- > net/sunrpc/svcsock.c | 6 ++++++ > 1 files changed, 6 insertions(+), 0 deletions(-) > > diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c > index 0c81202..ec19444 100644 > --- a/net/sunrpc/svcsock.c > +++ b/net/sunrpc/svcsock.c > @@ -414,6 +414,7 @@ static void svc_udp_data_ready(struct sock *sk) > set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags); > svc_xprt_enqueue(&svsk->sk_xprt); > } > + smp_mb(); > if (wq && waitqueue_active(wq)) > wake_up_interruptible(wq); > }
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