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From: Taylor Blau <me@ttaylorr.com>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: git@vger.kernel.org, Junio C Hamano <gitster@pobox.com>,
	Emily Shaffer <emilyshaffer@google.com>
Subject: Re: [PATCH 4/6] tr2: fix memory leak & logic error in 2f732bf15e6
Date: Wed, 25 Aug 2021 23:21:34 -0400	[thread overview]
Message-ID: <YScIvuySaXPcBb/Y@nand.local> (raw)
In-Reply-To: <patch-4.6-73e7d4eb6ac-20210825T231400Z-avarab@gmail.com>

On Thu, Aug 26, 2021 at 01:19:22AM +0200, Ævar Arnfjörð Bjarmason wrote:
> In a subsequent commit I'll be replacing most of this code to log N
> parents, but let's first fix bugs introduced in the recent
> 2f732bf15e6 (tr2: log parent process name, 2021-07-21).
>
> It was using the strbuf_read_file() in the wrong way, its return value
> is either a length or a negative value on error. If we didn't have a
> procfs, or otherwise couldn't access it we'd end up pushing an empty
> string to the trace2 ancestry array.

Sure, and I could believe that we didn't ever test the "couldn't open
/proc/pid/comm" case, which explains why this error didn't fail any
tests. I wondered whether it was worth writing this instead as:

    if (strbuf_read_file(...) < 0)
      warning(...);

before trimming and pushing the result onto "names", but we should
probably be swallowing this case and not presenting it as an error
(since it's completely acceptable to not be able to read from comm,
e.g., in versions of procfs on Linux older than 2.6.33).

> It was also using the strvec_push() API the wrong way. That API always
> does an xstrdup(), so by detaching the strbuf here we'd leak
> memory. Let's instead pass in our pointer for strvec_push() to
> xstrdup(), and then free our own strbuf.

Right, you could make strvec_push_nodup() non-static, but I don't think
that kind of churn is worthwhile.

> Furthermore we need to free that "procfs_path" strbuf whether or not
> strbuf_read_file() succeeds, which was another source of memory leaks
> in 2f732bf15e6, i.e. we'd leak that memory as well if we weren't on a
> system where we could read the file from procfs.

Hmm. It's completely correct to only call strbuf_release on names inside
of the body of the if statement, but it's extra work for the reader to
figure that out. Why not put both strbuf_release() calls next to each
other (immediately before the return) to make it more obvious (since
freeing the STRBUF_INIT value is a noop)?

Thanks,
Taylor

  reply	other threads:[~2021-08-26  3:21 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-07  0:29 [PATCH] tr2: log parent process name Emily Shaffer
2021-05-07  3:25 ` Bagas Sanjaya
2021-05-07 17:09 ` Emily Shaffer
2021-05-10 12:29 ` Ævar Arnfjörð Bjarmason
2021-05-11 21:31   ` Junio C Hamano
2021-05-14 22:06   ` Emily Shaffer
2021-05-16  3:48     ` Junio C Hamano
2021-05-17 20:17       ` Emily Shaffer
2021-05-11 17:28 ` Jeff Hostetler
2021-05-14 22:07   ` Emily Shaffer
2021-05-20 21:05 ` [PATCH v2] " Emily Shaffer
2021-05-20 21:36   ` Randall S. Becker
2021-05-20 23:23     ` Emily Shaffer
2021-05-21 13:20       ` Randall S. Becker
2021-05-21 16:24         ` Randall S. Becker
2021-05-21  2:09   ` Junio C Hamano
2021-05-21 19:02     ` Emily Shaffer
2021-05-21 23:22       ` Junio C Hamano
2021-05-24 18:37         ` Emily Shaffer
2021-05-21 19:15   ` Jeff Hostetler
2021-05-21 20:05     ` Emily Shaffer
2021-05-21 20:23       ` Randall S. Becker
2021-05-22 11:18       ` Jeff Hostetler
2021-05-24 23:33       ` Ævar Arnfjörð Bjarmason
2021-05-24 20:10   ` [PATCH v3] " Emily Shaffer
2021-05-24 20:49     ` Emily Shaffer
2021-05-25  3:54     ` Junio C Hamano
2021-05-25 13:33       ` Randall S. Becker
2021-06-08 18:58     ` [PATCH v4] " Emily Shaffer
2021-06-08 20:56       ` Emily Shaffer
2021-06-08 22:10       ` [PATCH v5] " Emily Shaffer
2021-06-08 22:16         ` Randall S. Becker
2021-06-08 22:24           ` Emily Shaffer
2021-06-08 22:39             ` Randall S. Becker
2021-06-09 20:17               ` Emily Shaffer
2021-06-16  8:42         ` Junio C Hamano
2021-06-28 16:45         ` Jeff Hostetler
2021-06-29 23:51           ` Emily Shaffer
2021-06-30  6:10             ` Ævar Arnfjörð Bjarmason
2021-07-22  0:21               ` Emily Shaffer
2021-07-22  1:27         ` [PATCH v6 0/2] " Emily Shaffer
2021-07-22  1:27           ` [PATCH v6 1/2] tr2: make process info collection platform-generic Emily Shaffer
2021-08-02  9:34             ` Ævar Arnfjörð Bjarmason
2021-07-22  1:27           ` [PATCH v6 2/2] tr2: log parent process name Emily Shaffer
2021-07-22 21:02             ` Junio C Hamano
2021-08-02  9:38             ` Ævar Arnfjörð Bjarmason
2021-08-02 12:45               ` Ævar Arnfjörð Bjarmason
2021-08-02 10:22             ` Ævar Arnfjörð Bjarmason
2021-08-02 12:47               ` Ævar Arnfjörð Bjarmason
2021-08-02 15:23               ` Jeff Hostetler
2021-08-02 16:10               ` Randall S. Becker
2021-08-02 18:41                 ` Ævar Arnfjörð Bjarmason
2021-08-25 23:19               ` [PATCH 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-25 23:19                 ` [PATCH 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-26  3:09                   ` Taylor Blau
2021-08-25 23:19                 ` [PATCH 4/6] tr2: fix memory leak & logic error in 2f732bf15e6 Ævar Arnfjörð Bjarmason
2021-08-26  3:21                   ` Taylor Blau [this message]
2021-08-25 23:19                 ` [PATCH 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-26  3:23                   ` Taylor Blau
2021-08-25 23:19                 ` [PATCH 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-25 23:49                   ` Eric Sunshine
2021-08-26  4:07                   ` Taylor Blau
2021-08-26 12:24                     ` "I don't know what the author meant by that..." (was "Re: [PATCH 6/6] tr2: log N parent process names on Linux") Ævar Arnfjörð Bjarmason
2021-08-26 12:22                 ` [PATCH v2 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 4/6] tr2: fix memory leak & logic error in 2f732bf15e6 Ævar Arnfjörð Bjarmason
2021-08-26 15:58                     ` Eric Sunshine
2021-08-26 16:42                     ` Junio C Hamano
2021-08-26 12:22                   ` [PATCH v2 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-26 12:22                   ` [PATCH v2 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-26 22:38                   ` [PATCH v2 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Taylor Blau
2021-08-27  8:02                   ` [PATCH v3 " Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 1/6] tr2: remove NEEDSWORK comment for "non-procfs" implementations Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 2/6] tr2: clarify TRACE2_PROCESS_INFO_EXIT comment under Linux Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 3/6] tr2: stop leaking "thread_name" memory Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 4/6] tr2: leave the parent list empty upon failure & don't leak memory Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 5/6] tr2: do compiler enum check in trace2_collect_process_info() Ævar Arnfjörð Bjarmason
2021-08-27  8:02                     ` [PATCH v3 6/6] tr2: log N parent process names on Linux Ævar Arnfjörð Bjarmason
2021-08-31  0:17                     ` [PATCH v3 0/6] tr2: plug memory leaks + logic errors + Win32 & Linux feature parity Taylor Blau
2021-08-02 10:30             ` [PATCH v6 2/2] tr2: log parent process name Ævar Arnfjörð Bjarmason
2021-08-02 16:24               ` Junio C Hamano
2021-08-02 18:42                 ` Ævar Arnfjörð Bjarmason
2021-07-22 16:59           ` [PATCH v6 0/2] " Jeff Hostetler

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