User-Agent: Microsoft-MacOutlook/16.56.21121100
Date:   Thu, 30 Dec 2021 10:42:28 +0800
Subject: Re: Lock problems in linux/tools/perf/util/dso.c
From:   Ryan Cai <ycaibb@gmail.com>
To:     Namhyung Kim <namhyung@kernel.org>
CC:     Adrian Hunter <adrian.hunter@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Message-ID: <64E36F38-E037-4561-8E0C-B288674A5BD9@gmail.com>
Thread-Topic: Lock problems in linux/tools/perf/util/dso.c
References: <4C0186FE-729D-4F77-947D-11933BA38818@gmail.com>
 <CAM9d7ciroZswudPXAAs9Zo3_veFMugJJZ4XZWhGSKHdFPcDOjQ@mail.gmail.com>
In-Reply-To: <CAM9d7ciroZswudPXAAs9Zo3_veFMugJJZ4XZWhGSKHdFPcDOjQ@mail.gmail.com>
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Hi, Namhyung,

1. Indeed, I got wrong here.
2. Yes, the branch should be if (pthread_mutex_lock(&dso__data_open_lock))=20
instead of if (pthread_mutex_lock(&dso__data_open_lock) < 0).

Could I send a patch?

Best,
Ryan

=EF=BB=BFOn 30/12/2021, 3:08 AM, "Namhyung Kim" <namhyung@kernel.org> wrote:

    Hello,

    On Wed, Dec 22, 2021 at 3:33 AM Ryan Cai <ycaibb@gmail.com> wrote:
    >
    > Hi, I found a potential lock problem in dso_data_get_fd. Because the =
inconsistent branch conditions of pthread_mutex_lock(&dso__data_open_lock) a=
nd pthread_mutex_unlock(&dso__data_open_lock), it is possible that the lock =
dso__data_open_lock is not released in the dso_data_get_fd. Also, I have a q=
uestion on why the branch condition of pthread_mutex_lock(&dso__data_open_lo=
ck) is <0. I think that the branch condition should be !=3D0, because pthread_=
mutex_lock would return 0 when succeeding. Looking forward to further discus=
sion. One this bug is confirmed, I can send a patch.

    Please fix your mail client to wrap around 80 characters.

    1. dso__data_get_fd() should be paired with dso__data_put_fd()
       when it returns non-negative.  It'd unlock the mutex.

    2. I've checked the man page and it seems you're right.
       It just says that it'd return an error number or zero.

       https://linux.die.net/man/3/pthread_mutex_lock

    Thanks,
    Namhyung


    >
    >
    >
    > https://github.com/torvalds/linux/blob/e851dfae4371d3c751f1e18e8eb5eb=
a993de1467/tools/perf/util/dso.c#L708-L722
    >
    >
    >
    > Best,
    >
    > Ryan
    >
    >
    >
    >