Thanks for all your replies, the all_proc lock is held in pfind(..) at the point PROC_LOCK(p) is obtained. In the kern_wait(..) code below, the allproc_lock is acquired before removing the proc from the list of all procs. The PROC_LOCK is then acquired before continuing. Since the thread that called pfind(..) has the PROC_LOCK, kern_wait(..) would need to wait for it to release the PROC_LOCK before continuing. I hope this understanding is correct.
In http://fxr.watson.org/fxr/source/kern/kern_exit.c?v=RELENG62#L579 sx_xlock(&allproc_lock); 675 LIST_REMOVE(p, p_list); /* off zombproc */ 676 sx_xunlock(&allproc_lock); 677 LIST_REMOVE(p, p_sibling); 678 leavepgrp(p); 679 sx_xunlock(&proctree_lock); 680 681 /* 682 * As a side effect of this lock, we know that 683 * all other writes to this proc are visible now, so 684 * no more locking is needed for p. 685 */ 686 PROC_LOCK(p); -----Original Message----- From: Giorgos Keramidas [mailto:[EMAIL PROTECTED] Sent: Tuesday, April 01, 2008 10:58 AM To: Rao, Nikhil Cc: Roman Divacky; freebsd-hackers@freebsd.org Subject: Re: pfind() and the proc structure On Tue, 1 Apr 2008 07:23:58 -0700, "Rao, Nikhil" <[EMAIL PROTECTED]> wrote: > Ok, I should have caught that :-( Another question - Now that the > PROC_LOCK on p is obtained the all_proc lock is released and the > function returns, at this point can't the proc get deallocated ? > > Nikhil > > 242 struct proc * > 243 pfind(pid) > 244 register pid_t pid; > 245 { > 246 register struct proc *p; > 247 > 248 sx_slock(&allproc_lock); > 249 LIST_FOREACH(p, PIDHASH(pid), p_hash) > 250 if (p->p_pid == pid) { > 251 if (p->p_state == PRS_NEW) { > 252 p = NULL; > 253 break; > 254 } > 255 PROC_LOCK(p); > 256 break; > 257 } > 258 sx_sunlock(&allproc_lock); > 259 return (p); > 260 } Not until you unlock the specific proc entry. You are holding a lock for the specific proc entry, so anyone trying to `reap' the process would have to wait until you are done with what you are doing. _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
