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From: "Martin Ågren" <martin.agren@gmail.com>
To: Stefan Beller <sbeller@google.com>
Cc: "git@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: tsan: t5400: set_try_to_free_routine
Date: Tue, 15 Aug 2017 20:44:24 +0200	[thread overview]
Message-ID: <CAN0heSpPihOcXgP-iCkBFvvP2x-8=oxYGUFJbUhF8mwcYfgoxA@mail.gmail.com> (raw)
In-Reply-To: <CAGZ79kYbPvmqV1PR_NjxLbp2vqC6=JdP+-hzdwQvUmVLZU_Wtg@mail.gmail.com>

On 15 August 2017 at 19:35, Stefan Beller <sbeller@google.com> wrote:
> On Tue, Aug 15, 2017 at 5:53 AM, Martin Ågren <martin.agren@gmail.com> wrote:
>> Using SANITIZE=thread made t5400-send-pack.sh hit the potential race
>> below.
>>
>> This is set_try_to_free_routine in wrapper.c. The race relates to the
>> reading of the "old" value. The caller doesn't care about the "old"
>> value, so this should be harmless right now. But it seems that using
>> this mechanism from multiple threads and restoring the earlier value
>> will probably not work out every time. (Not necessarily because of the
>> race in set_try_to_free_routine, but, e.g., because callers might not
>> restore the function pointer in the reverse order of how they
>> originally set it.)
>>
>> Properly "fixing" this for thread-safety would probably require some
>> redesigning, which at the time might not be warranted. I'm just posting
>> this for completeness.
>
> Maybe related read (also error handling in threads):
> https://public-inbox.org/git/20170619220036.22656-1-avarab@gmail.com/

Thanks for the pointer. Threading is tricky business, indeed. I still
haven't entirely groked all the users of set_try_to_free_routine, i.e.,
what they want to avoid and what they want to achieve. I'm just happy
that the only user which cares about the old value is not threaded, to
the best of my understanding.

  reply	other threads:[~2017-08-15 18:44 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 ` tsan: t3008: hashmap_add touches size from multiple threads Martin Ågren
2017-08-15 17:59   ` 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 [this message]
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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