From 12fb39ec3e6bc529feff3ba2862c6a4a30bd54eb Mon Sep 17 00:00:00 2001 From: Mark Johnston Date: Tue, 1 Mar 2022 11:48:39 -0500 Subject: [PATCH] proc: Relax proc_rwmem()'s assertion on the process hold count This reference ensures that the process and its associated vmspace will not be destroyed while proc_rwmem() is executing. If, however, the calling thread belongs to the target process, then it is unnecessary to hold the process. In particular, fasttrap - a module which enables userspace dtrace - may frequently call proc_rwmem(), and we'd prefer to avoid the overhead of locking and bumping the hold count when possible. Thus, make the assertion conditional on "p != curproc". Also assert that the process is not already exiting. No functional change intended. MFC after: 2 weeks Sponsored by: The FreeBSD Foundation --- sys/kern/sys_process.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c index 582bff962f1..8d8c5a1d34f 100644 --- a/sys/kern/sys_process.c +++ b/sys/kern/sys_process.c @@ -336,11 +336,12 @@ proc_rwmem(struct proc *p, struct uio *uio) int error, fault_flags, page_offset, writing; /* - * Assert that someone has locked this vmspace. (Should be - * curthread but we can't assert that.) This keeps the process - * from exiting out from under us until this operation completes. + * Make sure that the process' vmspace remains live. */ - PROC_ASSERT_HELD(p); + if (p != curproc) + PROC_ASSERT_HELD(p); + KASSERT((p->p_flag & P_WEXIT) == 0, + ("%s: process %p is exiting", __func__, p)); PROC_LOCK_ASSERT(p, MA_NOTOWNED); /* -- 2.45.2