On Mon, Sep 21, 2020 at 07:37:13PM +0200, Marco Elver wrote: > On Mon, 21 Sep 2020 at 19:13, Paul E. McKenney <paul...@kernel.org> wrote: > > > > On Mon, Sep 21, 2020 at 03:26:11PM +0200, Marco Elver wrote: > > > Add KFENCE test suite, testing various error detection scenarios. Makes > > > use of KUnit for test organization. Since KFENCE's interface to obtain > > > error reports is via the console, the test verifies that KFENCE outputs > > > expected reports to the console. > > > > > > Reviewed-by: Dmitry Vyukov <dvyu...@google.com> > > > Co-developed-by: Alexander Potapenko <gli...@google.com> > > > Signed-off-by: Alexander Potapenko <gli...@google.com> > > > Signed-off-by: Marco Elver <el...@google.com> > > > > [ . . . ] > > > > > +/* Test SLAB_TYPESAFE_BY_RCU works. */ > > > +static void test_memcache_typesafe_by_rcu(struct kunit *test) > > > +{ > > > + const size_t size = 32; > > > + struct expect_report expect = { > > > + .type = KFENCE_ERROR_UAF, > > > + .fn = test_memcache_typesafe_by_rcu, > > > + }; > > > + > > > + setup_test_cache(test, size, SLAB_TYPESAFE_BY_RCU, NULL); > > > + KUNIT_EXPECT_TRUE(test, test_cache); /* Want memcache. */ > > > + > > > + expect.addr = test_alloc(test, size, GFP_KERNEL, ALLOCATE_ANY); > > > + *expect.addr = 42; > > > + > > > + rcu_read_lock(); > > > + test_free(expect.addr); > > > + KUNIT_EXPECT_EQ(test, *expect.addr, (char)42); > > > + rcu_read_unlock(); > > > > It won't happen very often, but memory really could be freed at this point, > > especially in CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels ... > > Ah, thanks for pointing it out. > > > > + /* No reports yet, memory should not have been freed on access. */ > > > + KUNIT_EXPECT_FALSE(test, report_available()); > > > > ... so the above statement needs to go before the rcu_read_unlock(). > > You mean the comment (and not the KUNIT_EXPECT_FALSE that no reports > were generated), correct? > > Admittedly, the whole comment is a bit imprecise, so I'll reword.
I freely confess that I did not research exactly what might generate a report. But if this KUNIT_EXPECT_FALSE() was just verifying that the previous KUNIT_EXPECT_TRUE() did not trigger, then yes, the code is just fine as it is. Thanx, Paul > > > + rcu_barrier(); /* Wait for free to happen. */ > > > > But you are quite right that the memory is not -guaranteed- to be freed > > until we get here. > > Right, I'll update the comment. > > Thanks, > -- Marco