Re: Lock problems in linux/tools/perf/util/dso.c

[Ryan Cai]

Hi, Namhyung,

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

Could I send a patch?

Best,
Ryan

On 30/12/2021, 3:08 AM, "Namhyung Kim" <namhyung@xxxxxxxxxx> wrote:

    Hello,

    On Wed, Dec 22, 2021 at 3:33 AM Ryan Cai <ycaibb@xxxxxxxxx> 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) and 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 question on why the branch condition of pthread_mutex_lock(&dso__data_open_lock) is <0. I think that the branch condition should be !=0, because pthread_mutex_lock would return 0 when succeeding. Looking forward to further discussion. 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


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    > https://github.com/torvalds/linux/blob/e851dfae4371d3c751f1e18e8eb5eba993de1467/tools/perf/util/dso.c#L708-L722
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    >
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    > Best,
    >
    > Ryan
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    >