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From: "Martin Ågren" <martin.agren@gmail.com>
To: git@vger.kernel.org
Cc: Jeff Hostetler <jeffhost@microsoft.com>
Subject: tsan: t3008: hashmap_add touches size from multiple threads
Date: Tue, 15 Aug 2017 14:53:06 +0200	[thread overview]
Message-ID: <adb37b70139fd1e2bac18bfd22c8b96683ae18eb.1502780344.git.martin.agren@gmail.com> (raw)
In-Reply-To: <cover.1502780343.git.martin.agren@gmail.com>

Using SANITIZE=thread made t3008-ls-files-lazy-init-name-hash.sh hit
the potential race below.

What seems to happen is, threaded_lazy_init_name_hash ends up using
hashmap_add on the_index.dir_hash from two threads in a way that tsan
considers racy. While the buckets each have their own mutex, the "size"
does not. So it might end up with the wrong (lower) value. The size is
used to determine when to resize, but that should be fine, since
resizing is turned off due to threading anyway.

If the size is ever used for something else, the consequences might
range from cosmetic error to devastating. I have a "feeling" the size is
not used at the time, although maybe it is, in some roundabout way which
I'm not seeing.

Martin

WARNING: ThreadSanitizer: data race (pid=10554)
  Read of size 4 at 0x00000082d488 by thread T2 (mutexes: write M16):
    #0 hashmap_add hashmap.c:209 (test-lazy-init-name-hash+0x000000438b7d)
    #1 hash_dir_entry_with_parent_and_prefix name-hash.c:302 (test-lazy-init-name-hash+0x00000043ea6c)
    #2 handle_range_dir name-hash.c:347 (test-lazy-init-name-hash+0x00000043ea6c)
    #3 handle_range_1 name-hash.c:415 (test-lazy-init-name-hash+0x00000043ea6c)
    #4 lazy_dir_thread_proc name-hash.c:471 (test-lazy-init-name-hash+0x00000043ea6c)
    #5 <null> <null> (libtsan.so.0+0x0000000230d9)

  Previous write of size 4 at 0x00000082d488 by thread T1 (mutexes: write M31):
    #0 hashmap_add hashmap.c:209 (test-lazy-init-name-hash+0x000000438b90)
    #1 hash_dir_entry_with_parent_and_prefix name-hash.c:302 (test-lazy-init-name-hash+0x00000043e0f2)
    #2 handle_range_dir name-hash.c:347 (test-lazy-init-name-hash+0x00000043e0f2)
    #3 handle_range_1 name-hash.c:415 (test-lazy-init-name-hash+0x00000043e0f2)
    #4 handle_range_dir name-hash.c:380 (test-lazy-init-name-hash+0x00000043e709)
    #5 handle_range_1 name-hash.c:415 (test-lazy-init-name-hash+0x00000043e709)
    #6 lazy_dir_thread_proc name-hash.c:471 (test-lazy-init-name-hash+0x00000043e709)
    #7 <null> <null> (libtsan.so.0+0x0000000230d9)

  Location is global 'the_index' of size 208 at 0x00000082d400 (test-lazy-init-name-hash+0x00000082d488)

  Mutex M16 (0x7d640001a5b8) created at:
    #0 pthread_mutex_init <null> (libtsan.so.0+0x0000000280b5)
    #1 init_recursive_mutex thread-utils.c:73 (test-lazy-init-name-hash+0x0000004d829b)
    #2 init_dir_mutex name-hash.c:241 (test-lazy-init-name-hash+0x00000043d714)
    #3 threaded_lazy_init_name_hash name-hash.c:526 (test-lazy-init-name-hash+0x00000043d714)
    #4 lazy_init_name_hash name-hash.c:588 (test-lazy-init-name-hash+0x00000043d714)
    #5 lazy_init_name_hash name-hash.c:581 (test-lazy-init-name-hash+0x00000043ec34)
    #6 test_lazy_init_name_hash name-hash.c:613 (test-lazy-init-name-hash+0x00000043ec34)
    #7 time_runs t/helper/test-lazy-init-name-hash.c:74 (test-lazy-init-name-hash+0x000000405ac2)
    #8 cmd_main t/helper/test-lazy-init-name-hash.c:261 (test-lazy-init-name-hash+0x0000004066c1)
    #9 main common-main.c:43 (test-lazy-init-name-hash+0x000000404f91)

  Mutex M31 (0x7d640001a810) created at:
    #0 pthread_mutex_init <null> (libtsan.so.0+0x0000000280b5)
    #1 init_recursive_mutex thread-utils.c:73 (test-lazy-init-name-hash+0x0000004d829b)
    #2 init_dir_mutex name-hash.c:241 (test-lazy-init-name-hash+0x00000043d714)
    #3 threaded_lazy_init_name_hash name-hash.c:526 (test-lazy-init-name-hash+0x00000043d714)
    #4 lazy_init_name_hash name-hash.c:588 (test-lazy-init-name-hash+0x00000043d714)
    #5 lazy_init_name_hash name-hash.c:581 (test-lazy-init-name-hash+0x00000043ec34)
    #6 test_lazy_init_name_hash name-hash.c:613 (test-lazy-init-name-hash+0x00000043ec34)
    #7 time_runs t/helper/test-lazy-init-name-hash.c:74 (test-lazy-init-name-hash+0x000000405ac2)
    #8 cmd_main t/helper/test-lazy-init-name-hash.c:261 (test-lazy-init-name-hash+0x0000004066c1)
    #9 main common-main.c:43 (test-lazy-init-name-hash+0x000000404f91)

  Thread T2 (tid=10557, running) created by main thread at:
    #0 pthread_create <null> (libtsan.so.0+0x000000027577)
    #1 threaded_lazy_init_name_hash name-hash.c:541 (test-lazy-init-name-hash+0x00000043d7ab)
    #2 lazy_init_name_hash name-hash.c:588 (test-lazy-init-name-hash+0x00000043d7ab)
    #3 lazy_init_name_hash name-hash.c:581 (test-lazy-init-name-hash+0x00000043ec34)
    #4 test_lazy_init_name_hash name-hash.c:613 (test-lazy-init-name-hash+0x00000043ec34)
    #5 time_runs t/helper/test-lazy-init-name-hash.c:74 (test-lazy-init-name-hash+0x000000405ac2)
    #6 cmd_main t/helper/test-lazy-init-name-hash.c:261 (test-lazy-init-name-hash+0x0000004066c1)
    #7 main common-main.c:43 (test-lazy-init-name-hash+0x000000404f91)

  Thread T1 (tid=10556, finished) created by main thread at:
    #0 pthread_create <null> (libtsan.so.0+0x000000027577)
    #1 threaded_lazy_init_name_hash name-hash.c:541 (test-lazy-init-name-hash+0x00000043d7ab)
    #2 lazy_init_name_hash name-hash.c:588 (test-lazy-init-name-hash+0x00000043d7ab)
    #3 lazy_init_name_hash name-hash.c:581 (test-lazy-init-name-hash+0x00000043ec34)
    #4 test_lazy_init_name_hash name-hash.c:613 (test-lazy-init-name-hash+0x00000043ec34)
    #5 time_runs t/helper/test-lazy-init-name-hash.c:74 (test-lazy-init-name-hash+0x000000405ac2)
    #6 cmd_main t/helper/test-lazy-init-name-hash.c:261 (test-lazy-init-name-hash+0x0000004066c1)
    #7 main common-main.c:43 (test-lazy-init-name-hash+0x000000404f91)

SUMMARY: ThreadSanitizer: data race hashmap.c:209 hashmap_add


  parent reply	other threads:[~2017-08-15 12:53 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-15 12:53 [PATCH/RFC 0/5] Some ThreadSanitizer-results Martin Ågren
2017-08-15 12:53 ` [PATCH 1/5] convert: initialize attr_action in convert_attrs Martin Ågren
2017-08-15 14:17   ` Torsten Bögershausen
2017-08-15 14:29     ` Torsten Bögershausen
2017-08-15 14:40     ` Martin Ågren
2017-08-15 12:53 ` [PATCH 2/5] pack-objects: take lock before accessing `remaining` Martin Ågren
2017-08-15 19:50   ` Johannes Sixt
2017-08-15 12:53 ` [PATCH 3/5] Makefile: define GIT_THREAD_SANITIZER Martin Ågren
2017-08-15 12:53 ` [PATCH 4/5] strbuf_reset: don't write to slopbuf with ThreadSanitizer Martin Ågren
2017-08-15 18:43   ` Junio C Hamano
2017-08-15 19:06     ` Martin Ågren
2017-08-15 19:19       ` Junio C Hamano
2017-08-15 12:53 ` [PATCH 5/5] ThreadSanitizer: add suppressions Martin Ågren
2017-08-15 12:53 ` Martin Ågren [this message]
2017-08-15 17:59   ` tsan: t3008: hashmap_add touches size from multiple threads Jeff Hostetler
2017-08-15 18:17     ` Stefan Beller
2017-08-15 18:40       ` Martin Ågren
2017-08-15 18:48         ` Stefan Beller
2017-08-15 19:21           ` Martin Ågren
2017-08-15 20:46             ` Jeff Hostetler
2017-08-30 18:59   ` [PATCH] hashmap: address ThreadSanitizer concerns Jeff Hostetler
2017-08-30 18:59     ` [PATCH] hashmap: add API to disable item counting when threaded Jeff Hostetler
2017-09-01 23:31       ` Johannes Schindelin
2017-09-01 23:50         ` Jonathan Nieder
2017-09-05 16:39           ` Jeff Hostetler
2017-09-05 17:13             ` Martin Ågren
2017-09-02  8:17         ` Jeff King
2017-09-04 15:59           ` Johannes Schindelin
2017-09-05 16:54           ` Jeff Hostetler
2017-09-06  3:43           ` Junio C Hamano
2017-09-05 16:33         ` Jeff Hostetler
2017-09-02  8:05       ` Jeff King
2017-09-05 17:07         ` Jeff Hostetler
2017-09-02  8:39       ` Simon Ruderich
2017-09-06  1:24       ` Junio C Hamano
2017-09-06 15:33         ` Jeff Hostetler
2017-09-06 15:43     ` [PATCH v2] hashmap: address ThreadSanitizer concerns Jeff Hostetler
2017-09-06 15:43       ` [PATCH v2] hashmap: add API to disable item counting when threaded Jeff Hostetler
2017-08-15 12:53 ` tsan: t5400: set_try_to_free_routine Martin Ågren
2017-08-15 17:35   ` Stefan Beller
2017-08-15 18:44     ` Martin Ågren
2017-08-17 10:57   ` Jeff King
2017-08-20 10:06 ` [PATCH/RFC 0/5] Some ThreadSanitizer-results Jeff King
2017-08-20 10:45   ` Martin Ågren
2017-08-21 17:43 ` [PATCH v2 0/4] " Martin Ågren
2017-08-21 17:43   ` [PATCH v2 1/4] convert: always initialize attr_action in convert_attrs Martin Ågren
2017-08-21 17:43   ` [PATCH v2 2/4] pack-objects: take lock before accessing `remaining` Martin Ågren
2017-08-21 17:43   ` [PATCH v2 3/4] strbuf_setlen: don't write to strbuf_slopbuf Martin Ågren
2017-08-23 17:24     ` Junio C Hamano
2017-08-23 17:43       ` Martin Ågren
2017-08-23 18:30         ` Junio C Hamano
2017-08-23 20:37     ` Brandon Casey
2017-08-23 21:04       ` Junio C Hamano
2017-08-23 21:20         ` Brandon Casey
2017-08-23 21:54           ` Brandon Casey
2017-08-23 22:11             ` Brandon Casey
2017-08-24 16:52             ` Junio C Hamano
2017-08-24 18:29               ` Brandon Casey
2017-08-24 19:16                 ` Martin Ågren
2017-08-23 22:24           ` Junio C Hamano
2017-08-23 22:39             ` Brandon Casey
2017-08-21 17:43   ` [PATCH v2 4/4] ThreadSanitizer: add suppressions Martin Ågren
2017-08-25 17:04     ` Jeff King
2017-08-28 20:56   ` [PATCH v2 0/4] Some ThreadSanitizer-results Jeff Hostetler

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