Explicitly wire the user buffer rather than doing it implicitly in

sbuf_new_for_sysctl(9).  This allows using an sbuf with a SYSCTL_OUT
drain for extremely large amounts of data where the caller knows that
appropriate references are held, and sleeping is not an issue.

Inspired by:	rwatson

share/man/man9/sbuf.9

@@ -177,9 +177,9 @@ The
 function will set up an sbuf with a drain function to use
 .Fn SYSCTL_OUT
 when the internal buffer fills.
-The sysctl old buffer will be wired, which allows for doing an
-.Fn sbuf_printf
-while holding a mutex.
+Note that if the various functions which append to an sbuf are used while
+a non-sleepable lock is held, the user buffer should be wired using
+.Fn sysctl_wire_old_buffer .
 .Pp
 The
 .Fn sbuf_delete

sys/dev/cxgb/cxgb_sge.c

@@ -3251,7 +3251,9 @@ t3_dump_rspq(SYSCTL_HANDLER_ARGS)
 	err = t3_sge_read_rspq(qs->port->adapter, rspq->cntxt_id, data);
 	if (err)
 		return (err);
-
+	err = sysctl_wire_old_buffer(req, 0);
+	if (err)
+		return (err);
 	sb = sbuf_new_for_sysctl(NULL, NULL, QDUMP_SBUF_SIZE, req);
 
 	sbuf_printf(sb, " \n index=%u size=%u MSI-X/RspQ=%u intr enable=%u intr armed=%u\n",
@@ -3316,7 +3318,9 @@ t3_dump_txq_eth(SYSCTL_HANDLER_ARGS)
 	err = t3_sge_read_ecntxt(qs->port->adapter, qs->rspq.cntxt_id, data);
 	if (err)
 		return (err);
-	
+	err = sysctl_wire_old_buffer(req, 0);
+	if (err)
+		return (err);
 	sb = sbuf_new_for_sysctl(NULL, NULL, QDUMP_SBUF_SIZE, req);
 
 	sbuf_printf(sb, " \n credits=%u GTS=%u index=%u size=%u rspq#=%u cmdq#=%u\n",
@@ -3381,6 +3385,9 @@ t3_dump_txq_ctrl(SYSCTL_HANDLER_ARGS)
 		return (EINVAL);
 	}
 
+	err = sysctl_wire_old_buffer(req, 0);
+	if (err != 0)
+		return (err);
 	sb = sbuf_new_for_sysctl(NULL, NULL, QDUMP_SBUF_SIZE, req);
 	sbuf_printf(sb, " qid=%d start=%d -> end=%d\n", qs->idx,
 	    txq->txq_dump_start,

sys/kern/kern_malloc.c

@@ -862,6 +862,9 @@ sysctl_kern_malloc_stats(SYSCTL_HANDLER_ARGS)
 	int error, i;
 	struct sbuf sbuf;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 	mtx_lock(&malloc_mtx);
 
@@ -1019,6 +1022,9 @@ sysctl_kern_mprof(SYSCTL_HANDLER_ARGS)
 	waste = 0;
 	mem = 0;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 	sbuf_printf(&sbuf, 
 	    "\n  Size                    Requests  Real Size\n");

sys/kern/kern_sysctl.c

@@ -1591,7 +1591,8 @@ userland_sysctl(struct thread *td, int *name, u_int namelen, void *old,
 }
 
 /*
- * Drain into a sysctl struct.  The user buffer must be wired.
+ * Drain into a sysctl struct.  The user buffer should be wired if a page
+ * fault would cause issue.
  */
 static int
 sbuf_sysctl_drain(void *arg, const char *data, int len)
@@ -1609,9 +1610,6 @@ sbuf_new_for_sysctl(struct sbuf *s, char *buf, int length,
     struct sysctl_req *req)
 {
 
-	/* Wire the user buffer, so we can write without blocking. */
-	sysctl_wire_old_buffer(req, 0);
-
 	s = sbuf_new(s, buf, length, SBUF_FIXEDLEN);
 	sbuf_set_drain(s, sbuf_sysctl_drain, req);
 	return (s);

sys/kern/subr_lock.c

@@ -393,6 +393,9 @@ dump_lock_prof_stats(SYSCTL_HANDLER_ARGS)
 	int error, cpu, t;
 	int enabled;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sb = sbuf_new_for_sysctl(NULL, NULL, LPROF_SBUF_SIZE, req);
 	sbuf_printf(sb, "\n%8s %9s %11s %11s %11s %6s %6s %2s %6s %s\n",
 	    "max", "wait_max", "total", "wait_total", "count", "avg", "wait_avg", "cnt_hold", "cnt_lock", "name");

sys/kern/subr_sleepqueue.c

@@ -1130,6 +1130,9 @@ dump_sleepq_prof_stats(SYSCTL_HANDLER_ARGS)
 	int error;
 	int i;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sb = sbuf_new_for_sysctl(NULL, NULL, SLEEPQ_SBUFSIZE, req);
 	sbuf_printf(sb, "\nwmesg\tcount\n");
 	enabled = prof_enabled;

sys/kern/subr_witness.c

@@ -2544,6 +2544,10 @@ sysctl_debug_witness_fullgraph(SYSCTL_HANDLER_ARGS)
 		return (error);
 	}
 	error = 0;
+
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sb = sbuf_new_for_sysctl(NULL, NULL, FULLGRAPH_SBUF_SIZE, req);
 	if (sb == NULL)
 		return (ENOMEM);

sys/vm/uma_core.c

@@ -3224,6 +3224,9 @@ sysctl_vm_zone_stats(SYSCTL_HANDLER_ARGS)
 	uma_keg_t k;
 	int count, error, i;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 
 	count = 0;

sys/vm/vm_phys.c

@@ -125,6 +125,9 @@ sysctl_vm_phys_free(SYSCTL_HANDLER_ARGS)
 	struct vm_freelist *fl;
 	int error, flind, oind, pind;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 	for (flind = 0; flind < vm_nfreelists; flind++) {
 		sbuf_printf(&sbuf, "\nFREE LIST %d:\n"
@@ -161,6 +164,9 @@ sysctl_vm_phys_segs(SYSCTL_HANDLER_ARGS)
 	struct vm_phys_seg *seg;
 	int error, segind;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 	for (segind = 0; segind < vm_phys_nsegs; segind++) {
 		sbuf_printf(&sbuf, "\nSEGMENT %d:\n\n", segind);
@@ -187,8 +193,11 @@ sysctl_vm_phys_lookup_lists(SYSCTL_HANDLER_ARGS)
 	struct sbuf sbuf;
 	int domain, error, flind, ndomains;
 
-	ndomains = vm_nfreelists - VM_NFREELIST + 1;
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
+	ndomains = vm_nfreelists - VM_NFREELIST + 1;
 	for (domain = 0; domain < ndomains; domain++) {
 		sbuf_printf(&sbuf, "\nDOMAIN %d:\n\n", domain);
 		for (flind = 0; flind < vm_nfreelists; flind++)

sys/vm/vm_reserv.c

@@ -182,6 +182,9 @@ sysctl_vm_reserv_partpopq(SYSCTL_HANDLER_ARGS)
 	vm_reserv_t rv;
 	int counter, error, level, unused_pages;
 
+	error = sysctl_wire_old_buffer(req, 0);
+	if (error != 0)
+		return (error);
 	sbuf_new_for_sysctl(&sbuf, NULL, 128, req);
 	sbuf_printf(&sbuf, "\nLEVEL     SIZE  NUMBER\n\n");
 	for (level = -1; level <= VM_NRESERVLEVEL - 2; level++) {