cvs commit: src/sys/compat/linux linux_misc.c
rwatson at FreeBSD.org
Sat Aug 19 15:42:36 UTC 2006
On Sat, 19 Aug 2006, Alexander Leidinger wrote:
> Quoting Robert Watson <rwatson at FreeBSD.org> (Fri, 18 Aug 2006 18:47:12 +0100 (BST)):
>> On Thu, 17 Aug 2006, Alexander Leidinger wrote:
>>> - protect td->td_proc->p_pid with the proc lock in linux_getpid
>>> in the amd64 (= non i386) case 
>> Is this necessary? In principle, td->td_proc is static for a live thread
>> bound to a process (i.e., in a system call, which the current thread
>> presumable is, as long as td == curthread), p_pid is static for a live
>> process that isn't exiting (so in a system call is not generally exiting).
>> The native FreeBSD getpid() only acquires the process lock when following
>> p_pptr, since this can change during a system call (i.e., as a result of
>> the parent dying, and the child being re-parented to init(8)).
> Now that you tell me this, I have the impression that I have mixed up p_pid
> with p_pptr here... I have to have a look at the code again.
In the general case, following many p->p_foo fields does require the process
lock, as the process might exit, etc, while you're accessing the fields. The
exception for curthread->td_proc relates to fields that are static as long as
the process isn't exiting. Fields with this property are marked with (b) in
the locking guide in proc.h.
Robert N M Watson
University of Cambridge
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