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kselftest: introduce new epoll test case
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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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Max Neunhoeffer <[email protected]>
Cc: Jakub Kicinski <[email protected]>
Cc: Christopher Kohlhoff <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Jason Baron <[email protected]>
Cc: Jes Sorensen <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
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Roman Penyaev authored and torvalds committed Apr 7, 2020
1 parent 16b7f3c commit 282144e
Showing 1 changed file with 66 additions and 1 deletion.
67 changes: 66 additions & 1 deletion tools/testing/selftests/filesystems/epoll/epoll_wakeup_test.c
Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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

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