Turn console printf buffering into a kernel option and only on

by default for sun4v where it is absolutely required.

This change moves the buffer from struct pcpu to the stack to avoid
using the critical section which created a LOR in a couple of cases
due to interaction with the tty code and kqueue. The LOR can't be
fixed with the critical section and the pcpu buffer can't be used
without the critical section.

Putting the buffer on the stack was my initial solution, but it was
pointed out that the stress on the stack might cause problems
depending on the call path. We don't have a way of creating tests
for those possible cases, so it's best to leave this as an option
for the time being. In time we may get enough data to enable this
option more generally.

sys/amd64/amd64/genassym.c

@@ -185,7 +185,6 @@ ASSYM(PC_CURTHREAD, offsetof(struct pcpu, pc_curthread));
 ASSYM(PC_FPCURTHREAD, offsetof(struct pcpu, pc_fpcurthread));
 ASSYM(PC_IDLETHREAD, offsetof(struct pcpu, pc_idlethread));
 ASSYM(PC_CURPCB, offsetof(struct pcpu, pc_curpcb));
-ASSYM(PC_CONS_BUFR, offsetof(struct pcpu, pc_cons_bufr));
 ASSYM(PC_CPUID, offsetof(struct pcpu, pc_cpuid));
 ASSYM(PC_SCRATCH_RSP, offsetof(struct pcpu, pc_scratch_rsp));
 ASSYM(PC_CURPMAP, offsetof(struct pcpu, pc_curpmap));

sys/arm/arm/genassym.c

@@ -69,7 +69,6 @@ ASSYM(PCB_R12, offsetof(struct pcb, un_32.pcb32_r12));
 ASSYM(PCB_PC, offsetof(struct pcb, un_32.pcb32_pc));
 ASSYM(PCB_SP, offsetof(struct pcb, un_32.pcb32_sp));
 
-ASSYM(PC_CONS_BUFR, offsetof(struct pcpu, pc_cons_bufr));
 ASSYM(PC_CURPCB, offsetof(struct pcpu, pc_curpcb));
 ASSYM(PC_CURTHREAD, offsetof(struct pcpu, pc_curthread));
 ASSYM(M_LEN, offsetof(struct mbuf, m_len));

sys/conf/options

@@ -709,6 +709,9 @@ SC_PIXEL_MODE		opt_syscons.h
 SC_RENDER_DEBUG		opt_syscons.h
 SC_TWOBUTTON_MOUSE	opt_syscons.h
 
+# options for printf
+PRINTF_BUFR_SIZE	opt_printf.h
+
 # kbd options
 KBD_DISABLE_KEYMAP_LOAD	opt_kbd.h
 KBD_INSTALL_CDEV	opt_kbd.h

sys/i386/i386/genassym.c

@@ -195,7 +195,6 @@ ASSYM(PC_COMMON_TSSD, offsetof(struct pcpu, pc_common_tssd));
 ASSYM(PC_TSS_GDT, offsetof(struct pcpu, pc_tss_gdt));
 ASSYM(PC_FSGS_GDT, offsetof(struct pcpu, pc_fsgs_gdt));
 ASSYM(PC_CURRENTLDT, offsetof(struct pcpu, pc_currentldt));
-ASSYM(PC_CONS_BUFR, offsetof(struct pcpu, pc_cons_bufr));
 ASSYM(PC_CPUID, offsetof(struct pcpu, pc_cpuid));
 ASSYM(PC_CURPMAP, offsetof(struct pcpu, pc_curpmap));
 ASSYM(PC_PRIVATE_TSS, offsetof(struct pcpu, pc_private_tss));

sys/kern/subr_prf.c

@@ -38,6 +38,7 @@
 __FBSDID("$FreeBSD$");
 
 #include "opt_ddb.h"
+#include "opt_printf.h"
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -291,18 +292,24 @@ printf(const char *fmt, ...)
 	va_list ap;
 	struct putchar_arg pca;
 	int retval;
-
-	critical_enter();
+#ifdef PRINTF_BUFR_SIZE
+	char bufr[PRINTF_BUFR_SIZE];
+#endif
 
 	va_start(ap, fmt);
 	pca.tty = NULL;
 	pca.flags = TOCONS | TOLOG;
 	pca.pri = -1;
-	pca.p_bufr = (char *) PCPU_PTR(cons_bufr);
+#ifdef PRINTF_BUFR_SIZE
+	pca.p_bufr = bufr;
 	pca.p_next = pca.p_bufr;
-	pca.n_bufr = PCPU_CONS_BUFR;
-	pca.remain = PCPU_CONS_BUFR;
+	pca.n_bufr = sizeof(bufr);
+	pca.remain = sizeof(bufr);
 	*pca.p_next = '\0';
+#else
+	/* Don't buffer console output. */
+	pca.p_bufr = NULL;
+#endif
 
 	retval = kvprintf(fmt, putchar, &pca, 10, ap);
 	va_end(ap);
@@ -314,8 +321,6 @@ printf(const char *fmt, ...)
 	if (!panicstr)
 		msgbuftrigger = 1;
 
-	critical_exit();
-
 	return (retval);
 }
 
@@ -324,17 +329,23 @@ vprintf(const char *fmt, va_list ap)
 {
 	struct putchar_arg pca;
 	int retval;
-
-	critical_enter();
+#ifdef PRINTF_BUFR_SIZE
+	char bufr[PRINTF_BUFR_SIZE];
+#endif
 
 	pca.tty = NULL;
 	pca.flags = TOCONS | TOLOG;
 	pca.pri = -1;
-	pca.p_bufr = (char *) PCPU_PTR(cons_bufr);
+#ifdef PRINTF_BUFR_SIZE
+	pca.p_bufr = bufr;
 	pca.p_next = pca.p_bufr;
-	pca.n_bufr = PCPU_CONS_BUFR;
-	pca.remain = PCPU_CONS_BUFR;
+	pca.n_bufr = sizeof(bufr);
+	pca.remain = sizeof(bufr);
 	*pca.p_next = '\0';
+#else
+	/* Don't buffer console output. */
+	pca.p_bufr = NULL;
+#endif
 
 	retval = kvprintf(fmt, putchar, &pca, 10, ap);
 
@@ -345,8 +356,6 @@ vprintf(const char *fmt, va_list ap)
 	if (!panicstr)
 		msgbuftrigger = 1;
 
-	critical_exit();
-
 	return (retval);
 }
 

sys/powerpc/powerpc/genassym.c

@@ -55,7 +55,6 @@
 #include <machine/pmap.h>
 #include <machine/sigframe.h>
 
-ASSYM(PC_CONS_BUFR, offsetof(struct pcpu, pc_cons_bufr));
 ASSYM(PC_CURTHREAD, offsetof(struct pcpu, pc_curthread));
 ASSYM(PC_CURPCB, offsetof(struct pcpu, pc_curpcb));
 ASSYM(PC_CURPMAP, offsetof(struct pcpu, pc_curpmap));

sys/sparc64/sparc64/genassym.c

@@ -198,7 +198,6 @@ ASSYM(HASH_ENTRY_SHIFT, HASH_ENTRY_SHIFT);
 
 ASSYM(V_INTR, offsetof(struct vmmeter, v_intr));
 
-ASSYM(PC_CONS_BUFR, offsetof(struct pcpu, pc_cons_bufr));
 ASSYM(PC_CURTHREAD, offsetof(struct pcpu, pc_curthread));
 ASSYM(PC_CURPCB, offsetof(struct pcpu, pc_curpcb));
 ASSYM(PC_CPUID, offsetof(struct pcpu, pc_cpuid));

sys/sun4v/conf/GENERIC

@@ -59,6 +59,7 @@ options 	_KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real-time extensions
 options 	AHC_REG_PRETTY_PRINT	# Print register bitfields in debug
 					# output.  Adds ~128k to driver.
 options 	ADAPTIVE_GIANT		# Giant mutex is adaptive.
+options 	PRINTF_BUFR_SIZE=128	# Prevent printf output being interspersed.
 
 # Debugging for use in -current
 options 	KDB			# Enable kernel debugger support.

sys/sys/pcpu.h

@@ -48,9 +48,6 @@
 struct pcb;
 struct thread;
 
-/* Size of the per-cpu console buffer for printf(). */
-#define	PCPU_CONS_BUFR	128
-
 /*
  * This structure maps out the global data that needs to be kept on a
  * per-cpu basis.  The members are accessed via the PCPU_GET/SET/PTR
@@ -74,8 +71,6 @@ struct pcpu {
 	int		pc_ktr_idx;		/* Index into trace table */
 	char		*pc_ktr_buf;
 #endif
-	char		pc_cons_bufr[PCPU_CONS_BUFR];
-						/* Console buffer */
 	PCPU_MD_FIELDS;
 	struct vmmeter	pc_cnt;			/* VM stats counters */
 	struct device	*pc_device;