# HG changeset patch
# User Taylor R Campbell <riastradh@NetBSD.org>
# Date 1588599693 0
#      Mon May 04 13:41:33 2020 +0000
# Branch trunk
# Node ID 1a3123a0eccca17da2e90a931aabe01a5601924a
# Parent  4d90033727a1bbba57854aaf5ac2d4f675184468
Release the collision if we find one.

Candidate fix for:

panic: lock error: Mutex: mutex_vector_enter,542: locking against myself: lock 0xffff8f611abd37e0 cpu 8 lwp 0xffff8f60a3c6a040
cpu8: Begin traceback...
vpanic() at netbsd:vpanic+0x178
snprintf() at netbsd:snprintf
lockdebug_abort() at netbsd:lockdebug_abort+0xe6
mutex_vector_enter() at netbsd:mutex_vector_enter+0x3c1
ksem_close_fop() at netbsd:ksem_close_fop+0x17
closef() at netbsd:closef+0x69
fd_free() at netbsd:fd_free+0x101
exit1() at netbsd:exit1+0x118
sys_exit() at netbsd:sys_exit+0x3d
syscall() at netbsd:syscall+0x299

diff -r 4d90033727a1 -r 1a3123a0eccc sys/kern/uipc_sem.c
--- a/sys/kern/uipc_sem.c	Mon May 04 00:18:34 2020 +0000
+++ b/sys/kern/uipc_sem.c	Mon May 04 13:41:33 2020 +0000
@@ -110,6 +110,7 @@ static kauth_listener_t	ksem_listener;
 static int		ksem_sysinit(void);
 static int		ksem_sysfini(bool);
 static int		ksem_modcmd(modcmd_t, void *);
+static void		ksem_release(ksem_t *, int);
 static int		ksem_close_fop(file_t *);
 static int		ksem_stat_fop(file_t *, struct stat *);
 static int		ksem_read_fop(file_t *, off_t *, struct uio *,
@@ -365,6 +366,7 @@ ksem_lookup_pshared(intptr_t id)
 static void
 ksem_alloc_pshared_id(ksem_t *ksem)
 {
+	ksem_t *ksem0;
 	uint32_t try;
 
 	KASSERT(ksem->ks_pshared_proc != NULL);
@@ -374,10 +376,11 @@ ksem_alloc_pshared_id(ksem_t *ksem)
 		try = (cprng_fast32() & ~KSEM_MARKER_MASK) |
 		    KSEM_PSHARED_MARKER;
 
-		if (ksem_lookup_pshared_locked(try) == NULL) {
+		if ((ksem0 = ksem_lookup_pshared_locked(try)) == NULL) {
 			/* Got it! */
 			break;
 		}
+		ksem_release(ksem0, -1);
 	}
 	ksem->ks_pshared_id = try;
 	u_long bucket = KSEM_PSHARED_HASH(ksem->ks_pshared_id);