git: 76dcbd770d7b - stable/13 - proc: Relax proc_rwmem()'s assertion on the process hold count

The branch stable/13 has been updated by markj:

URL: https://cgit.FreeBSD.org/src/commit/?id=76dcbd770d7b1e37e3fe14472d9f339b9180ebd8

commit 76dcbd770d7b1e37e3fe14472d9f339b9180ebd8
Author:     Mark Johnston <markj@FreeBSD.org>
AuthorDate: 2022-03-01 16:48:39 +0000
Commit:     Mark Johnston <markj@FreeBSD.org>
CommitDate: 2022-03-15 15:39:55 +0000

    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.
    
    Sponsored by:   The FreeBSD Foundation
    
    (cherry picked from commit 12fb39ec3e6bc529feff3ba2862c6a4a30bd54eb)
---
 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 1b9c00179bda..273adca19a0d 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -215,11 +215,12 @@ 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);
 
 	/*