Rich,
On 12/19/2014 03:05 AM, Rich Felker wrote:
> The man page for tgkill claims:
>
> "If tgid is specified as -1, tgkill() is equivalent to tkill()."
>
> However, the kernel source contains:
>
> /* This is only valid for single tasks */
> if (pid <= 0 || tgid <= 0)
> return -EINVAL;
>
> and I confirmed that passing -1 results in EINVAL. This discrepency
> should be fixed in the documentation.
Sigh. Text along those lines has been there since the pages added
in 2003.
> Since there's therefore no way to achieve the same behavior as tkill
> using the tgkill syscall, I'd also like to request a removal of the
> text claiming tkill is obsolete. tgkill does not solve the race
> condition it claims to solve (this is documented to some extent in the
> relevant git commits to musl libc, and I intend to write more on the
> issue later) nor is it needed to solve the race (tkill works just as
> well if used correctly).
I guess the relevant bug here is
http://sourceware.org/bugzilla/show_bug.cgi?id=12889
right?
I'm a little puzzled. In that bug report, you say:
(The tgkill syscall was designed to eliminate a similar race
condition in tkill, but it only succeeded in eliminating races
where the tid gets reused in a different process, and does not
help if the same tid gets assigned to a new thread in the
same process.)
Is it not the case that tgkill() solves *some* of the race conditions
that tkill() is vulnerable to (i.e., TID recycled in a different
process), and therefore is an improvement on tkill() (i.e., renders
it obsolete)?
Cheers,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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