On Fri, 11 May 2012, Xin LI wrote:
Log: ??Revert previous revision, misunderstood the code :(Modified: ??head/sys/kern/kern_kthread.c Modified: head/sys/kern/kern_kthread.c ============================================================================== --- head/sys/kern/kern_kthread.c ?? ?? ?? ??Fri May 11 23:41:52 2012 ?? ?? ?? ??(r235300) +++ head/sys/kern/kern_kthread.c ?? ?? ?? ??Fri May 11 23:43:32 2012 ?? ?? ?? ??(r235301) @@ -182,7 +182,6 @@ kproc_suspend(struct proc *p, int timo) ?? ?? ?? ?? ?? ?? ?? ??return (EINVAL); ?? ?? ?? ??} ?? ?? ?? ??SIGADDSET(p->p_siglist, SIGSTOP); - ?? ?? ?? PROC_UNLOCK(p); ?? ?? ?? ??wakeup(p); ?? ?? ?? ??return msleep(&p->p_siglist, &p->p_mtx, PPAUSE | PDROP, "suspkp", timo);
Please don't use mailer clients that corrupt whitespace to binary characters. The above is unreadable in vi (but i remember it from the original).
For the record, p->p_mtx is the mutex used by PROC_[UN]LOCK(), which has to be held while calling msleep().
Even if it weren't, dropping the lock before sleeping would give a classic race. Otherwise, PROC_UNLOCK() is a good obfuscation. p_mtx in the sleep call isn't similarly obfuscated. Some subsystems have a macro that obfuscates the name of their lock(s) too, but proc.h doesn't. kern/*.c has 23 hard-coded references of the form &somep->p_mtx. Bruce
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