From mboxrd@z Thu Jan 1 00:00:00 1970 From: Richard Palethorpe Date: Wed, 25 Nov 2020 13:23:54 +0000 Subject: [LTP] [PATCH] fzsync: skip test when avaliable CPUs less than 2 In-Reply-To: <04c4b073-6ad3-836a-7f63-7632a4e6ddb7@suse.cz> References: <20201125101633.30154-1-liwang@redhat.com> <87eekhof3i.fsf@suse.de> <04c4b073-6ad3-836a-7f63-7632a4e6ddb7@suse.cz> Message-ID: <87blflo9hx.fsf@suse.de> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: ltp@lists.linux.it Hello, Martin Doucha writes: > On 25. 11. 20 12:22, Richard Palethorpe wrote: >> Hello Li, >> >> Li Wang writes: >> >>> It makes no sense to run parallel thread to simulate race conditions on >>> system with CPU number less than two, especially for kvm guest, it does >>> not have any chance to get real parallel running and probably encounter >>> failure as below: >> >> Most of the tests using FuzzySync do not need true parallism. We were >> able to reproduce a number of race conditions on a single vCPU. Infact >> it may actually benefit some races because one thread has to pause to >> allow the other to run, perhaps creating a huge race window. >> >>> >>> === 100% reproducible on a 1cpu guest === >>> >>> cmdline="af_alg07" >>> contacts="" >>> analysis=exit >>> <<>> >>> tst_test.c:1248: TINFO: Timeout per run is 0h 05m 00s >>> ../../../include/tst_fuzzy_sync.h:507: TINFO: Minimum sampling period ended >>> ../../../include/tst_fuzzy_sync.h:330: TINFO: loop = 1024, delay_bias = 0 >>> ../../../include/tst_fuzzy_sync.h:318: TINFO: start_a - start_b: { avg = -137522ns, avg_dev = 854248ns, dev_ratio = 6.21 } >>> ../../../include/tst_fuzzy_sync.h:318: TINFO: end_a - start_a : { avg = 1915ns, avg_dev = 535ns, dev_ratio = 0.28 } >>> ../../../include/tst_fuzzy_sync.h:318: TINFO: end_b - start_b : { avg = 1885ns, avg_dev = 42ns, dev_ratio = 0.02 } >>> ../../../include/tst_fuzzy_sync.h:318: TINFO: end_a - end_b : { avg = -137492ns, avg_dev = 854818ns, dev_ratio = 6.22 } >>> ../../../include/tst_fuzzy_sync.h:318: TINFO: spins : { avg = 554786 , avg_dev = 7355 , dev_ratio = 0.01 } >>> ../../../include/tst_fuzzy_sync.h:636: TINFO: Exceeded execution time, requesting exit >>> af_alg07.c:96: TFAIL: fchownat() failed to fail, kernel may be vulnerable >>> >>> Signed-off-by: Li Wang >>> CC: Richard Palethorpe >>> --- >>> include/tst_fuzzy_sync.h | 3 +++ >>> 1 file changed, 3 insertions(+) >>> >>> diff --git a/include/tst_fuzzy_sync.h b/include/tst_fuzzy_sync.h >>> index 4141f5c64..2e864b312 100644 >>> --- a/include/tst_fuzzy_sync.h >>> +++ b/include/tst_fuzzy_sync.h >>> @@ -281,6 +281,9 @@ static void tst_init_stat(struct tst_fzsync_stat *s) >>> static void tst_fzsync_pair_reset(struct tst_fzsync_pair *pair, >>> void *(*run_b)(void *)) >>> { >>> + if (get_nprocs() < 2) >>> + tst_brk(TCONF, "Fuzzy Sync requires at least two CPUs available"); >>> + >>> tst_fzsync_pair_cleanup(pair); >>> >>> tst_init_stat(&pair->diff_ss); >> >> Perhaps this test would pass with more loops and a big enough delay >> range, but this is also wasting time on a single vCPU. I'm not sure >> whether we should filter this test at the LTP level; it may trigger the >> bug on some single CPU configs. > > No, af_alg07 requires 2 CPUs, otherwise it'll report false positives. > The test will pass only if fchownat() hits a half-closed socket and > returns error. But IIRC the half-closed socket will be destroyed during > reschedule which means there's no race window to hit anymore. But it > would be better to put the TCONF condition into the test itself. Interesting, I wonder if this is also true for the real-time kernel with the threads set to RT priority? -- Thank you, Richard.