Date: Tue, 1 Mar 2022 17:41:55 GMT From: Mark Johnston <markj@FreeBSD.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: git: 12fb39ec3e6b - main - proc: Relax proc_rwmem()'s assertion on the process hold count Message-ID: <202203011741.221Hftwu093303@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=12fb39ec3e6bc529feff3ba2862c6a4a30bd54eb commit 12fb39ec3e6bc529feff3ba2862c6a4a30bd54eb Author: Mark Johnston <markj@FreeBSD.org> AuthorDate: 2022-03-01 16:48:39 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2022-03-01 17:40:35 +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. 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 582bff962f1a..8d8c5a1d34ff 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); /*
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