Messages in this thread | | | Date | Mon, 24 Oct 2022 08:30:13 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH v1] perf record: Fix event fd races |
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Em Mon, Oct 24, 2022 at 05:16:56PM +0800, Leo Yan escreveu: > On Sun, Oct 23, 2022 at 10:33:30PM -0700, Ian Rogers wrote: > > [...] > > > > > +static volatile int done_fd = -1; > > > > > > Here is a bit suspecious for adding volatile qualifier. See the > > > document: process/volatile-considered-harmful.rst. > > > > > > I know the document is mainly for kernel programming, but seems to me > > > it's also valid for C programming in userspace. > > > > > > I not sure what's the purpose for adding volatile for done_fd, if we > > > really have concern for reading any stale value for done_fd, should we > > > use WRITE_ONCE/READ_ONCE? > > > > We could just switch to C11 and stdatomic. The volatile is consistent > > with the code above and more consistent with the expectation of > > writing to a variable that is read in a signal handler. > > Thanks for the info for C11 and stdatomic.h. The documentation [1] says > the safe way is for accessing shared data in signal handler is: > > static volatile sig_atomic_t done_fd = -1; > > It's fine if you want to use another patch to address this issue, this > patch for fixing errno is fine for me: > > Reviewed-by: Leo Yan <leo.yan@linaro.org>
Thanks, applied.
- Arnaldo
> [1] https://wiki.sei.cmu.edu/confluence/display/c/SIG31-C.+Do+not+access+shared+objects+in+signal+handlers
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- Arnaldo
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