[Bug 20762] New: epoll_wait(2): upper limit to timeout

[Bug 20762] New: epoll_wait(2): upper limit to timeout

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=20762

           Summary: epoll_wait(2): upper limit to timeout
           Product: Documentation
           Version: unspecified
    Kernel Version: n/a
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: man-pages
        AssignedTo: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
        ReportedBy: arnerup-UNjuZkX4dYU@public.gmane.org
        Regression: No


The timeout argument has an upper limit. Any values above that limit are
treated the same as -1, i.e. to wait indefinitely. The limit is given by:

#define EP_MAX_MSTIMEO min(1000ULL * MAX_SCHEDULE_TIMEOUT / HZ, (LONG_MAX -
999ULL) / HZ)

That is, the limit depends on the size of a long and the timer frequency.
Assuming the a long is never smaller than 32 bits and HZ never larger than
1000, the worst case is 35 minutes. I think this should be mentioned under
"BUGS".

Although this is likely to be fixed in the future
(http://lkml.org/lkml/2010/8/8/144), the problem exists in at least 2.6.14 -
2.6.35. I don't know if select(2) and poll(2) are affected.

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[Bug 20762] epoll_wait(2): upper limit to timeout

[bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r]

https://bugzilla.kernel.org/show_bug.cgi?id=20762


Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
         Resolution|                            |CODE_FIX




--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>  2012-08-16 09:33:31 ---
I aplied the following patch:

--- a/man2/epoll_wait.2
+++ b/man2/epoll_wait.2
@@ -198,6 +198,18 @@ If the new file descriptor becomes ready,
 it will cause the
 .BR epoll_wait ()
 call to unblock.
+.SH BUGS
+In kernels before 2.6.37, a
+.I timeout
+value larger than approximately
+.I LONG_MAX / HZ
+milliseconds is treated as \-1 (i.e., infinity).
+Thus, for example, on a system where the
+.I sizeof(long)
+is 4 and the kernel
+.I HZ
+value is 1000,
+this means that timeouts greater than 35.79 minutes are treated as infinity.
 .SH "SEE ALSO"
 .BR epoll_create (2),
 .BR epoll_ctl (2),

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