Date: Thu, 2 Nov 2023 13:40:04 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: eac624207ccf - main - Ensure "init" (PID 1) also executes userret() initially Message-ID: <202311021340.3A2De4ko027635@gitrepo.freebsd.org>
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The branch main has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=eac624207ccf3a16225368d226861b06e3631d0d commit eac624207ccf3a16225368d226861b06e3631d0d Author: Olivier Certner <olce.freebsd@certner.fr> AuthorDate: 2023-10-10 17:36:20 +0000 Commit: Mark Johnston <markj@FreeBSD.org> CommitDate: 2023-11-02 13:30:03 +0000 Ensure "init" (PID 1) also executes userret() initially Calling userret() from fork_return() misses the first return to userspace of the "init" (PID 1) process. The latter is indeed created by fork1() followed by a call to cpu_fork_kthread_handler() call that replaces fork_return() by start_init() as the function to execute after fork. A new process' initial return to userspace in the end always happens through returning from fork_exit(), so move userret() there instead to fix the omission. This problem was discovered as part of a revamp of scheduling priorities that lead to experimenting with asserting and sometimes resetting priorities in sched_userret(), in the course of which the author stumbled on panics being triggered only in init() or only in other processes, depending on the modifications to sched_userret(). This change currently has no practical effect but will have some in the near future. Reviewed by: markj, kib MFC after: 2 weeks Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D42257 --- sys/kern/kern_fork.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/sys/kern/kern_fork.c b/sys/kern/kern_fork.c index 3080bd11123d..6127b7f05fe0 100644 --- a/sys/kern/kern_fork.c +++ b/sys/kern/kern_fork.c @@ -1170,8 +1170,14 @@ fork_exit(void (*callout)(void *, struct trapframe *), void *arg, } mtx_assert(&Giant, MA_NOTOWNED); + /* + * Now going to return to userland. + */ + if (p->p_sysent->sv_schedtail != NULL) (p->p_sysent->sv_schedtail)(td); + + userret(td, frame); } /* @@ -1222,8 +1228,6 @@ fork_return(struct thread *td, struct trapframe *frame) if (!prison_isalive(td->td_ucred->cr_prison)) exit1(td, 0, SIGKILL); - userret(td, frame); - #ifdef KTRACE if (KTRPOINT(td, KTR_SYSRET)) ktrsysret(td->td_sa.code, 0, 0);
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