From 10af00f7a135c85796a9c4c75228358b8898da5c Mon Sep 17 00:00:00 2001 From: Siddhesh Poyarekar Date: Fri, 14 Mar 2025 10:18:21 -0400 Subject: [PATCH] tst-fopen-threaded: Only check EOF for failing read The fread race checker looks for EOF in every thread, which is incorrect since threads calling fread successfully could lag behind and read the EOF condition, resulting in multiple threads thinking that they encountered an EOF. Only look for EOF condition if fread fails to read a char. Also drop the clearerr() since it could mask the failure of another reader, thus hiding a test failure. Finally, also check for error in the stream for completeness. Signed-off-by: Siddhesh Poyarekar Reviewed-by: Florian Weimer --- sysdeps/pthread/tst-fopen-threaded.c | 28 ++++++++++++++++++---------- 1 file changed, 18 insertions(+), 10 deletions(-) diff --git a/sysdeps/pthread/tst-fopen-threaded.c b/sysdeps/pthread/tst-fopen-threaded.c index 5c792c93e3..ade58ad19e 100644 --- a/sysdeps/pthread/tst-fopen-threaded.c +++ b/sysdeps/pthread/tst-fopen-threaded.c @@ -64,19 +64,27 @@ threadReadRoutine (void *argv) /* Wait for all threads to be ready to read. */ xpthread_barrier_wait (&barrier); - ret = - fread (&read_buffer, sizeof (char), sizeof (read_buffer), my_data->fd); - if (feof (my_data->fd) != 0) + ret = fread (&read_buffer, 1, sizeof (read_buffer), my_data->fd); + /* If no data is returned (we read only 1 byte, so there's no short read + situation here), look for EOF flag and record it in MY_DATA. The EOF flag + is not cleared because that could result in a test failure being masked + when two threads fail to read and one of them clears error/EOF flags + before the second one has the chance to observe it. + + Successful readers could still see the EOF if they fall behind the failing + read when calling feof(), which could result in a false test failure. To + avoid this race, we only make the failing reader check for EOF or + error. */ + if (ret == 0) { - clearerr (my_data->fd); - my_data->eof = true; + if (feof (my_data->fd) != 0) + my_data->eof = true; + else + FAIL_EXIT1 ("fread failed (ferror: %d): %m", ferror (my_data->fd)); } else - { - TEST_COMPARE (ret, 1); - /* Save the read value. */ - my_data->value = read_buffer; - } + /* Save the read value. */ + my_data->value = read_buffer; TEST_COMPARE (ferror (my_data->fd), 0); return NULL; }