git: 47877889f2b8 - main - ddb ps: Use the pidhash to enumerate processes not in allproc.

[John Baldwin]

The branch main has been updated by jhb:

URL: https://cgit.FreeBSD.org/src/commit/?id=47877889f2b823f4c2fa135f5f3955ce0b3bdca1

commit 47877889f2b823f4c2fa135f5f3955ce0b3bdca1
Author:     John Baldwin <jhb at FreeBSD.org>
AuthorDate: 2021-01-01 00:00:05 +0000
Commit:     John Baldwin <jhb at FreeBSD.org>
CommitDate: 2021-01-01 00:00:05 +0000

    ddb ps: Use the pidhash to enumerate processes not in allproc.
    
    Exiting processes that have been removed from allproc but are still
    executing are not yet marked PRS_ZOMBIE, so they were not listed (for
    example, if a thread panics during exit1()).  To detect these
    processes, clear p_list.le_prev to NULL explicitly after removing a
    process from the allproc list and check for this sentinel rather than
    PRS_ZOMBIE when walking the pidhash.
    
    While here, simplify the pidhash walk to use a single outer loop.
    
    Reviewed by:    kib
    Sponsored by:   Netflix
    Differential Revision:  https://reviews.freebsd.org/D27824
---
 sys/ddb/db_ps.c      | 14 ++++++--------
 sys/kern/kern_exit.c |  9 +++++++++
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/sys/ddb/db_ps.c b/sys/ddb/db_ps.c
index df2db88e97a1..da655d11da02 100644
--- a/sys/ddb/db_ps.c
+++ b/sys/ddb/db_ps.c
@@ -107,7 +107,7 @@ void
 db_ps(db_expr_t addr, bool hasaddr, db_expr_t count, char *modif)
 {
 	struct proc *p;
-	int i, j;
+	int i;
 
 	ps_mode = modif[0] == 'a' ? PRINT_ARGS : PRINT_NONE;
 
@@ -125,14 +125,12 @@ db_ps(db_expr_t addr, bool hasaddr, db_expr_t count, char *modif)
 		db_ps_proc(p);
 
 	/*
-	 * Do zombies.
+	 * Processes such as zombies not in allproc.
 	 */
-	for (i = 0; i < pidhashlock + 1 && !db_pager_quit; i++) {
-		for (j = i; j <= pidhash && !db_pager_quit; j += pidhashlock + 1) {
-			LIST_FOREACH(p, &pidhashtbl[j], p_hash) {
-				if (p->p_state == PRS_ZOMBIE)
-					db_ps_proc(p);
-			}
+	for (i = 0; i <= pidhash && !db_pager_quit; i++) {
+		LIST_FOREACH(p, &pidhashtbl[i], p_hash) {
+			if (p->p_list.le_prev == NULL)
+				db_ps_proc(p);
 		}
 	}
 }
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 0e748751d019..e1b40a171345 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -39,6 +39,7 @@
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
+#include "opt_ddb.h"
 #include "opt_ktrace.h"
 
 #include <sys/param.h>
@@ -436,6 +437,14 @@ exit1(struct thread *td, int rval, int signo)
 	 */
 	sx_xlock(&allproc_lock);
 	LIST_REMOVE(p, p_list);
+
+#ifdef DDB
+	/*
+	 * Used by ddb's 'ps' command to find this process via the
+	 * pidhash.
+	 */
+	p->p_list.le_prev = NULL;
+#endif
 	sx_xunlock(&allproc_lock);
 
 	sx_xlock(&proctree_lock);