BUG #17095: ./configure fails thread_test.c when run under TSAN

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BUG #17095: ./configure fails thread_test.c when run under TSAN
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* BUG #17095: ./configure fails thread_test.c when run under TSAN
@ 2021-07-08 20:01  PG Bug reporting form <noreply@postgresql.org>
  0 siblings, 1 reply; 3+ messages in thread

From: PG Bug reporting form @ 2021-07-08 20:01 UTC (permalink / raw)
  To: pgsql-bugs@lists.postgresql.org; +Cc: vlovich+github@gmail.com

The following bug has been logged on the website:

Bug reference:      17095
Logged by:          Vitali Lovich
Email address:      vlovich+github@gmail.com
PostgreSQL version: 14beta2
Operating system:   Arch Linux
Description:        

When I run configure with -fsanitize=address (using clang 13 at revision
d3676d4b666ead794fc58bbc7e07aa406dcf487a), it errors out because
`thread_test.c` is violating thread safety.

Specifically it complains about the access of errno2_set, errno1_set,
thread1_done, & thread2_done being read/modified from multiple threads
without any kind of synchronization. AFAICT these TSAN errors are correct.

^ permalink  raw  reply  [nested|flat] 3+ messages in thread

* Re: BUG #17095: ./configure fails thread_test.c when run under TSAN
@ 2021-07-08 20:33  Vitali Lovich <vlovich@gmail.com>
  parent: PG Bug reporting form <noreply@postgresql.org>
  0 siblings, 1 reply; 3+ messages in thread

From: Vitali Lovich @ 2021-07-08 20:33 UTC (permalink / raw)
  To: Vitali Lovich <vlovich+github@gmail.com>; pgsql-bugs@lists.postgresql.org

I've confirmed the following patch (relative to
45b88269a353ad93744772791feb6d01bc7e1e42) resolves the issue. It's
predicated on the assumption that gcc or clang (or a compiler with the
relevant builtins) are being used to build this.

inline patch 1: src/test/thread/thread_test.c (+0/-0 lines) download inline-1.patch
diff --git a/src/test/thread/thread_test.c b/src/test/thread/thread_test.c
index 5392439146..cef8eb6c82 100644
--- a/src/test/thread/thread_test.c
+++ b/src/test/thread/thread_test.c
@@ -80,6 +80,14 @@ static volatile int thread2_done = 0;
static volatile int errno1_set = 0;
static volatile int errno2_set = 0;

+static void atomic_write(volatile int* ptr, int value) {
+       __atomic_store_n(ptr, value, __ATOMIC_RELAXED);
+}
+
+static int atomic_read(volatile int* ptr) {
+       return __atomic_load_n(ptr, __ATOMIC_RELAXED);
+}
+
#ifndef HAVE_STRERROR_R
static char *strerror_p1;
static char *strerror_p2;
@@ -163,7 +171,7 @@ main(int argc, char *argv[])
               exit(1);
       }

-       while (thread1_done == 0 || thread2_done == 0)
+       while (atomic_read(&thread1_done) == 0 ||
atomic_read(&thread2_done) == 0)
               sched_yield();                  /* if this is a portability
problem, remove it */

       /* Test things while we have thread-local storage */
@@ -312,8 +320,8 @@ func_call_1(void)
        * Wait for other thread to set errno. We can't use thread-specific
        * locking here because it might affect errno.
        */
-       errno1_set = 1;
-       while (errno2_set == 0)
+       atomic_write(&errno1_set, 1);
+       while (atomic_read(&errno2_set) == 0)
               sched_yield();

#ifdef WIN32
@@ -368,7 +376,7 @@ func_call_1(void)
       }
#endif

-       thread1_done = 1;
+       atomic_write(&thread1_done, 1);
       pthread_mutex_lock(&init_mutex);        /* wait for parent to test
*/
       pthread_mutex_unlock(&init_mutex);
}
@@ -403,8 +411,8 @@ func_call_2(void)
        * Wait for other thread to set errno. We can't use thread-specific
        * locking here because it might affect errno.
        */
-       errno2_set = 1;
-       while (errno1_set == 0)
+       atomic_write(&errno2_set, 1);
+       while (atomic_read(&errno1_set) == 0)
               sched_yield();

#ifdef WIN32
@@ -451,7 +459,7 @@ func_call_2(void)
       }
#endif

-       thread2_done = 1;
+       atomic_write(&thread2_done, 1);
       pthread_mutex_lock(&init_mutex);        /* wait for parent to test
*/
       pthread_mutex_unlock(&init_mutex);
}


I didn't predicate using the atomic on TSAN actually being used to build
this but that could also be done with something like:

#if defined(__has_feature)
#  if __has_feature(thread_sanitizer)
#    define ATOMIC_VOLATILES 1
#  endif
#endif

#if __SANITIZE_THREAD__
#define ATOMIC_VOLATILES 1
#endif

& fixing up the body of atomic_write/atomic_read to change behavior based on
#if ATOMIC_VOLATILES.

On Thu, Jul 8, 2021 at 1:02 PM PG Bug reporting form <noreply@postgresql.org>
wrote:

> The following bug has been logged on the website:
>
> Bug reference:      17095
> Logged by:          Vitali Lovich
> Email address:      vlovich+github@gmail.com
> PostgreSQL version: 14beta2
> Operating system:   Arch Linux
> Description:
>
> When I run configure with -fsanitize=address (using clang 13 at revision
> d3676d4b666ead794fc58bbc7e07aa406dcf487a), it errors out because
> `thread_test.c` is violating thread safety.
>
> Specifically it complains about the access of errno2_set, errno1_set,
> thread1_done, & thread2_done being read/modified from multiple threads
> without any kind of synchronization. AFAICT these TSAN errors are correct.
>
>

^ permalink  raw  reply  [nested|flat] 3+ messages in thread

* Re: BUG #17095: ./configure fails thread_test.c when run under TSAN
@ 2021-07-08 21:42  Tom Lane <tgl@sss.pgh.pa.us>
  parent: Vitali Lovich <vlovich@gmail.com>
  0 siblings, 0 replies; 3+ messages in thread

From: Tom Lane @ 2021-07-08 21:42 UTC (permalink / raw)
  To: Vitali Lovich <vlovich@gmail.com>; +Cc: pgsql-bugs@lists.postgresql.org

Vitali Lovich <vlovich@gmail.com> writes:
> I've confirmed the following patch (relative to
> 45b88269a353ad93744772791feb6d01bc7e1e42) resolves the issue. It's
> predicated on the assumption that gcc or clang (or a compiler with the
> relevant builtins) are being used to build this.

You realize of course that that assumption is *completely* untenable.

I'm inclined to say that if -fsanitize=address breaks configure,
then don't include -fsanitize=address in the CFLAGS you give to
configure.  It's hardly the first such restriction --- -Werror is
another one you can't inject that way, and I wouldn't be surprised
if there are more.

FWIW, I don't particularly agree with TSAN about the code being
incorrect.  On what platform is a fetch or a store of an int
not atomic?  (If there is one, Postgres will malfunction on it
anyway.)

			regards, tom lane

^ permalink  raw  reply  [nested|flat] 3+ messages in thread

end of thread, other threads:[~2021-07-08 21:42 UTC | newest]

Thread overview: 3+ messages (download: mbox mbox.gz follow: Atom feed)
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2021-07-08 20:01 BUG #17095: ./configure fails thread_test.c when run under TSAN PG Bug reporting form <noreply@postgresql.org>
2021-07-08 20:33 ` Vitali Lovich <vlovich@gmail.com>
2021-07-08 21:42   ` Tom Lane <tgl@sss.pgh.pa.us>

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