Messages in this thread | | | Date | Mon, 24 Oct 2022 17:16:56 +0800 | From | Leo Yan <> | Subject | Re: [PATCH v1] perf record: Fix event fd races |
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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>
[1] https://wiki.sei.cmu.edu/confluence/display/c/SIG31-C.+Do+not+access+shared+objects+in+signal+handlers
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