eventpoll: Annotate data-race of busy_poll_usecs

commit b9ca079dd6b09e08863aa998edf5c47597806c05 upstream.

A struct eventpoll's busy_poll_usecs field can be modified via a user
ioctl at any time. All reads of this field should be annotated with
READ_ONCE.

Fixes: 85455c795c07 ("eventpoll: support busy poll per epoll instance")
Cc: stable@vger.kernel.org
Signed-off-by: Martin Karsten <mkarsten@uwaterloo.ca>
Link: https://lore.kernel.org/r/20240806123301.167557-1-jdamato@fastly.com
Reviewed-by: Joe Damato <jdamato@fastly.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index f53ca4f7fceddd0b0e661f05105435b420e19430..6d0e2f547ae7d1ccf2f74ad9e6cb83db4fc27014 100644 (file)
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -420,7 +420,7 @@ static bool busy_loop_ep_timeout(unsigned long start_time,
 
 static bool ep_busy_loop_on(struct eventpoll *ep)
 {
-       return !!ep->busy_poll_usecs || net_busy_loop_on();
+       return !!READ_ONCE(ep->busy_poll_usecs) || net_busy_loop_on();
 }
 
 static bool ep_busy_loop_end(void *p, unsigned long start_time)