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

[Namhyung Kim]

Hello,

On Wed, Dec 22, 2021 at 3:33 AM Ryan Cai <ycaibb@xxxxxxxxx> wrote:
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> 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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> Best,
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> Ryan
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