Date: Mon, 2 Jan 2017 17:23:15 +0800 (CST) From: sdf <jiejinmv@163.com> To: freebsd-questions@freebsd.org Subject: when should we lock a process? Message-ID: <36a9d461.3f73.1595e7d6e67.Coremail.jiejinmv@163.com>
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Hi, friends. Can you see me?
I am new here and i am reading freebsd 11.0's kernel code since these days.
I don't know the purpose of this line of code:
=================
PROC_LOCK(p);
================
which is located at sys/kern/kern_exec.c line:394 function:do_execve().
And let me paste its context here:
387 /*
388 * Lock the process and set the P_INEXEC flag to indicate that
389 * it should be left alone until we're done here. This is
390 * necessary to avoid race conditions - e.g. in ptrace() -
391 * that might allow a local user to illicitly obtain elevated
392 * privileges.
393 */
394 PROC_LOCK(p);
395 KASSERT((p->p_flag & P_INEXEC) == 0,
396 ("%s(): process already has P_INEXEC flag", __func__));
397 p->p_flag |= P_INEXEC;
398 PROC_UNLOCK(p);
Could some one tell me when to lock a process? In another word, What are we doing when we are locking a process.
I can trace out its definition but i want to know more.
==================================
#define PROC_LOCK(p) mtx_lock(&(p)->p_mtx)
==================================
Thanks!
BTW: Is this maillist for kernel questions? If my question is not suitable here, could you tell me which maillist is for kernel developers?
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