From: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Subject: epoll: add a selftest for epoll timeout race Add a test case to ensure an event is observed by at least one poller when an epoll timeout is used. Link: https://lkml.kernel.org/r/20201028180202.952079-2-soheil.kdev@xxxxxxxxx Signed-off-by: Guantao Liu <guantaol@xxxxxxxxxx> Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx> Reviewed-by: Eric Dumazet <edumazet@xxxxxxxxxx> Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx> Reviewed-by: Khazhismel Kumykov <khazhy@xxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c | 95 ++++++++++ 1 file changed, 95 insertions(+) --- a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c~epoll-add-a-selftest-for-epoll-timeout-race +++ a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c @@ -3282,4 +3282,99 @@ TEST(epoll60) close(ctx.epfd); } +struct epoll61_ctx { + int epfd; + int evfd; +}; + +static void *epoll61_write_eventfd(void *ctx_) +{ + struct epoll61_ctx *ctx = ctx_; + int64_t l = 1; + + usleep(10950); + write(ctx->evfd, &l, sizeof(l)); + return NULL; +} + +static void *epoll61_epoll_with_timeout(void *ctx_) +{ + struct epoll61_ctx *ctx = ctx_; + struct epoll_event events[1]; + int n; + + n = epoll_wait(ctx->epfd, events, 1, 11); + /* + * If epoll returned the eventfd, write on the eventfd to wake up the + * blocking poller. + */ + if (n == 1) { + int64_t l = 1; + + write(ctx->evfd, &l, sizeof(l)); + } + return NULL; +} + +static void *epoll61_blocking_epoll(void *ctx_) +{ + struct epoll61_ctx *ctx = ctx_; + struct epoll_event events[1]; + + epoll_wait(ctx->epfd, events, 1, -1); + return NULL; +} + +TEST(epoll61) +{ + struct epoll61_ctx ctx; + struct epoll_event ev; + int i, r; + + ctx.epfd = epoll_create1(0); + ASSERT_GE(ctx.epfd, 0); + ctx.evfd = eventfd(0, EFD_NONBLOCK); + ASSERT_GE(ctx.evfd, 0); + + ev.events = EPOLLIN | EPOLLET | EPOLLERR | EPOLLHUP; + ev.data.ptr = NULL; + r = epoll_ctl(ctx.epfd, EPOLL_CTL_ADD, ctx.evfd, &ev); + ASSERT_EQ(r, 0); + + /* + * We are testing a race. Repeat the test case 1000 times to make it + * more likely to fail in case of a bug. + */ + for (i = 0; i < 1000; i++) { + pthread_t threads[3]; + int n; + + /* + * Start 3 threads: + * Thread 1 sleeps for 10.9ms and writes to the evenfd. + * Thread 2 calls epoll with a timeout of 11ms. + * Thread 3 calls epoll with a timeout of -1. + * + * The eventfd write by Thread 1 should either wakeup Thread 2 + * or Thread 3. If it wakes up Thread 2, Thread 2 writes on the + * eventfd to wake up Thread 3. + * + * If no events are missed, all three threads should eventually + * be joinable. + */ + ASSERT_EQ(pthread_create(&threads[0], NULL, + epoll61_write_eventfd, &ctx), 0); + ASSERT_EQ(pthread_create(&threads[1], NULL, + epoll61_epoll_with_timeout, &ctx), 0); + ASSERT_EQ(pthread_create(&threads[2], NULL, + epoll61_blocking_epoll, &ctx), 0); + + for (n = 0; n < ARRAY_SIZE(threads); ++n) + ASSERT_EQ(pthread_join(threads[n], NULL), 0); + } + + close(ctx.epfd); + close(ctx.evfd); +} + TEST_HARNESS_MAIN _
