git: 008b2e65442a - main - Make stop_all_proc_block interruptible to avoid deadlock with parallel suspension

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=008b2e65442a0d65bc5be9ca625616ddfa6f9ce2

commit 008b2e65442a0d65bc5be9ca625616ddfa6f9ce2
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2022-04-30 23:29:25 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2022-06-13 19:30:03 +0000

    Make stop_all_proc_block interruptible to avoid deadlock with parallel suspension
    
    If we try to single-thread a process which thread entered
    procctl(REAP_KILL_SUBTREE), and sleeping waiting for us unlocking
    stop_all_proc_blocker, we must be able to finish single-threading.  This
    requires the sleep to be interruptible.
    
    Reported and tested by: pho
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      2 weeks
    Differential revision:  https://reviews.freebsd.org/D35310
---
 sys/kern/kern_proc.c    | 7 ++++---
 sys/kern/kern_procctl.c | 4 ++--
 sys/sys/proc.h          | 2 +-
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/sys/kern/kern_proc.c b/sys/kern/kern_proc.c
index 6796d672afd7..67299472231a 100644
--- a/sys/kern/kern_proc.c
+++ b/sys/kern/kern_proc.c
@@ -3399,10 +3399,10 @@ static SYSCTL_NODE(_kern_proc, KERN_PROC_VM_LAYOUT, vm_layout, CTLFLAG_RD |
 static struct sx stop_all_proc_blocker;
 SX_SYSINIT(stop_all_proc_blocker, &stop_all_proc_blocker, "sapblk");
 
-void
+bool
 stop_all_proc_block(void)
 {
-	sx_xlock(&stop_all_proc_blocker);
+	return (sx_xlock_sig(&stop_all_proc_blocker) == 0);
 }
 
 void
@@ -3426,7 +3426,8 @@ stop_all_proc(void)
 	int r, gen;
 	bool restart, seen_stopped, seen_exiting, stopped_some;
 
-	stop_all_proc_block();
+	if (!stop_all_proc_block())
+		return;
 
 	cp = curproc;
 allproc_loop:
diff --git a/sys/kern/kern_procctl.c b/sys/kern/kern_procctl.c
index 6919fac71c5a..b6e48b46bb5c 100644
--- a/sys/kern/kern_procctl.c
+++ b/sys/kern/kern_procctl.c
@@ -1063,8 +1063,8 @@ kern_procctl(struct thread *td, idtype_t idtype, id_t id, int com, void *data)
 	sapblk = false;
 	if (cmd_info->sapblk != NULL) {
 		sapblk = cmd_info->sapblk(td, data);
-		if (sapblk)
-			stop_all_proc_block();
+		if (sapblk && !stop_all_proc_block())
+			return (ERESTART);
 	}
 
 	switch (cmd_info->lock_tree) {
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index cdb9cc17945d..5521f8321e2b 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -1238,7 +1238,7 @@ void	thread_unlink(struct thread *td);
 void	thread_unsuspend(struct proc *p);
 void	thread_wait(struct proc *p);
 
-void	stop_all_proc_block(void);
+bool	stop_all_proc_block(void);
 void	stop_all_proc_unblock(void);
 void	stop_all_proc(void);
 void	resume_all_proc(void);