Messages in this thread Patch in this message | | | Subject | Re: bug in sys_getpid() comment? | From | Robert Love <> | Date | 26 Sep 2002 23:45:10 -0400 |
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On Thu, 2002-09-26 at 23:21, Shaya Potter wrote:
> asmlinkage long sys_getpid(void) > { > /* This is SMP safe - current->pid doesn't change */ > return current->tgid; > } > > I assume we are returning tgid so that no matter what thread of a > multithreaded program calls getpid we return the same value, and that > the comment with pid is old and should have been updated when it was > changed to return tgid. A student in my Operating Systems class pointed > this out, so I figured no harm in pointing the possible bug out.
Yes, you are correct, the comment is wrong. We switched to returning the tgid in early 2.4 when CLONE_THREAD was introduced. The tgid and pid are identical unless CLONE_THREAD was used.
Attached patch fixes the typo and adds some comments explaining this. Marcelo, patch is against 2.4.20-pre8, please apply.
Robert Love
--- linux-2.4.20-pre8/kernel/timer.c Thu Sep 26 23:37:02 2002 +++ linux/kernel/timer.c Thu Sep 26 23:39:25 2002 @@ -740,10 +740,18 @@ * The Alpha uses getxpid, getxuid, and getxgid instead. Maybe this * should be moved into arch/i386 instead? */ - + +/** + * sys_getpid - return the thread group id of the current process + * + * Note, despite the name, this returns the tgid not the pid. The tgid and + * the pid are identical unless CLONE_THREAD was specified on clone() in + * which case the tgid is the same in all threads of the same group. + * + * This is SMP safe as current->tgid does not change. + */ asmlinkage long sys_getpid(void) { - /* This is SMP safe - current->pid doesn't change */ return current->tgid; } | |