kselftest: introduce new epoll test case

This testcase repeats epollbug.c from the bug:

  https://bugzilla.kernel.org/show_bug.cgi?id=205933

What it tests?  It tests the race between epoll_ctl() and epoll_wait().
New event mask passed to epoll_ctl() triggers wake up, which can be missed
because of the bug described in the link.  Reproduction is 100%, so easy
to fix.  Kudos, Max, for wonderful test case.

Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Max Neunhoeffer <max@arangodb.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Christopher Kohlhoff <chris.kohlhoff@clearpool.io>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Jes Sorensen <jes.sorensen@gmail.com>
Link: http://lkml.kernel.org/r/20200214170211.561524-2-rpenyaev@suse.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
index 37a04da..11eee0b 100644 (file)
--- a/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
+++ b/tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
@@ -7,13 +7,14 @@
 #include <pthread.h>
 #include <sys/epoll.h>
 #include <sys/socket.h>
+#include <sys/eventfd.h>
 #include "../../kselftest_harness.h"
 
 struct epoll_mtcontext
 {
        int efd[3];
        int sfd[4];
-       int count;
+       volatile int count;
 
        pthread_t main;
        pthread_t waiter;
@@ -3071,4 +3072,68 @@ TEST(epoll58)
        close(ctx.sfd[3]);
 }
 
+static void *epoll59_thread(void *ctx_)
+{
+       struct epoll_mtcontext *ctx = ctx_;
+       struct epoll_event e;
+       int i;
+
+       for (i = 0; i < 100000; i++) {
+               while (ctx->count == 0)
+                       ;
+
+               e.events = EPOLLIN | EPOLLERR | EPOLLET;
+               epoll_ctl(ctx->efd[0], EPOLL_CTL_MOD, ctx->sfd[0], &e);
+               ctx->count = 0;
+       }
+
+       return NULL;
+}
+
+/*
+ *        t0
+ *      (p) \
+ *           e0
+ *     (et) /
+ *        e0
+ *
+ * Based on https://bugzilla.kernel.org/show_bug.cgi?id=205933
+ */
+TEST(epoll59)
+{
+       pthread_t emitter;
+       struct pollfd pfd;
+       struct epoll_event e;
+       struct epoll_mtcontext ctx = { 0 };
+       int i, ret;
+
+       signal(SIGUSR1, signal_handler);
+
+       ctx.efd[0] = epoll_create1(0);
+       ASSERT_GE(ctx.efd[0], 0);
+
+       ctx.sfd[0] = eventfd(1, 0);
+       ASSERT_GE(ctx.sfd[0], 0);
+
+       e.events = EPOLLIN | EPOLLERR | EPOLLET;
+       ASSERT_EQ(epoll_ctl(ctx.efd[0], EPOLL_CTL_ADD, ctx.sfd[0], &e), 0);
+
+       ASSERT_EQ(pthread_create(&emitter, NULL, epoll59_thread, &ctx), 0);
+
+       for (i = 0; i < 100000; i++) {
+               ret = epoll_wait(ctx.efd[0], &e, 1, 1000);
+               ASSERT_GT(ret, 0);
+
+               while (ctx.count != 0)
+                       ;
+               ctx.count = 1;
+       }
+       if (pthread_tryjoin_np(emitter, NULL) < 0) {
+               pthread_kill(emitter, SIGUSR1);
+               pthread_join(emitter, NULL);
+       }
+       close(ctx.efd[0]);
+       close(ctx.sfd[0]);
+}
+
 TEST_HARNESS_MAIN