Re: PROBLEM: pthread-safety bug in write(2) on Linux 2.6.x

[Andrew Morton]

Dan Bonachea <bonachead@xxxxxxxxxxx> wrote:
>
> This problem arose in the parallel runtime system for a scientific language 
>  compiler (nearly a million lines of code total - definitely a "real-world" 
>  program) - the example code is merely a pared-down demonstration of the 
>  problem. In parallel scientific computing, it's very common for many threads 
>  to be writing to stdout (usually for monitoring purposes) and it's expected 
>  and normal for output from separate threads to be arbitrarily interleaved, but 
>  it's *not* ok for output to be lost entirely. This is essentially equivalent 
>  to the real-world example you gave of many threads logging to a file.

Interesting - afaik that's the first time this has been hit in a real
application.

>  We've worked around the problem in Linux 2.6 by adding locking at user-level 
>  around our writes, as you suggest, although this of course penalizes our 
>  performance on kernels that already correctly implement the thread-safety 
>  required by the POSIX spec. In any case it seemed like a problem that we 
>  should report, to be good open-source citizens - especially given that it 
>  appears to be a regression with respect to the Linux 2.4 kernel. How you 
>  choose to handle the report is of course your decision.

yup, thanks.
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