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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.

Signed-off-by: Guantao Liu <guantaol@google.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Khazhismel Kumykov <khazhy@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Link: https://lkml.kernel.org/r/20201028180202.952079-2-soheil.kdev@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Soheil Hassas Yeganeh 2020-11-01 17:08:07 -08:00 committed by Linus Torvalds
parent f8f6ae5d07
commit afabdf3338
1 changed files with 95 additions and 0 deletions
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95
tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
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@ -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