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linux-next/include/linux/console.h
Tejun Heo 8d91f8b153 printk: do cond_resched() between lines while outputting to consoles 
@console_may_schedule tracks whether console_sem was acquired through
lock or trylock.  If the former, we're inside a sleepable context and
console_conditional_schedule() performs cond_resched().  This allows
console drivers which use console_lock for synchronization to yield
while performing time-consuming operations such as scrolling.

However, the actual console outputting is performed while holding
irq-safe logbuf_lock, so console_unlock() clears @console_may_schedule
before starting outputting lines.  Also, only a few drivers call
console_conditional_schedule() to begin with.  This means that when a
lot of lines need to be output by console_unlock(), for example on a
console registration, the task doing console_unlock() may not yield for
a long time on a non-preemptible kernel.

If this happens with a slow console devices, for example a serial
console, the outputting task may occupy the cpu for a very long time.
Long enough to trigger softlockup and/or RCU stall warnings, which in
turn pile more messages, sometimes enough to trigger the next cycle of
warnings incapacitating the system.

Fix it by making console_unlock() insert cond_resched() between lines if
@console_may_schedule.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Calvin Owens <calvinowens@fb.com>
Acked-by: Jan Kara <jack@suse.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Kyle McMartin <kyle@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-01-16 11:17:25 -08:00

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/*
* linux/include/linux/console.h
*
* Copyright (C) 1993 Hamish Macdonald
*
* This file is subject to the terms and conditions of the GNU General Public
* License. See the file COPYING in the main directory of this archive
* for more details.
*
* Changed:
* 10-Mar-94: Arno Griffioen: Conversion for vt100 emulator port from PC LINUX
*/
#ifndef _LINUX_CONSOLE_H_
#define _LINUX_CONSOLE_H_ 1
#include <linux/types.h>
struct vc_data;
struct console_font_op;
struct console_font;
struct module;
struct tty_struct;
/*
* this is what the terminal answers to a ESC-Z or csi0c query.
*/
#define VT100ID "\033[?1;2c"
#define VT102ID "\033[?6c"
struct consw {
struct module *owner;
const char *(*con_startup)(void);
void (*con_init)(struct vc_data *, int);
void (*con_deinit)(struct vc_data *);
void (*con_clear)(struct vc_data *, int, int, int, int);
void (*con_putc)(struct vc_data *, int, int, int);
void (*con_putcs)(struct vc_data *, const unsigned short *, int, int, int);
void (*con_cursor)(struct vc_data *, int);
int (*con_scroll)(struct vc_data *, int, int, int, int);
void (*con_bmove)(struct vc_data *, int, int, int, int, int, int);
int (*con_switch)(struct vc_data *);
int (*con_blank)(struct vc_data *, int, int);
int (*con_font_set)(struct vc_data *, struct console_font *, unsigned);
int (*con_font_get)(struct vc_data *, struct console_font *);
int (*con_font_default)(struct vc_data *, struct console_font *, char *);
int (*con_font_copy)(struct vc_data *, int);
int (*con_resize)(struct vc_data *, unsigned int, unsigned int,
unsigned int);
int (*con_set_palette)(struct vc_data *, unsigned char *);
int (*con_scrolldelta)(struct vc_data *, int);
int (*con_set_origin)(struct vc_data *);
void (*con_save_screen)(struct vc_data *);
u8 (*con_build_attr)(struct vc_data *, u8, u8, u8, u8, u8, u8);
void (*con_invert_region)(struct vc_data *, u16 *, int);
u16 *(*con_screen_pos)(struct vc_data *, int);
unsigned long (*con_getxy)(struct vc_data *, unsigned long, int *, int *);
/*
* Prepare the console for the debugger. This includes, but is not
* limited to, unblanking the console, loading an appropriate
* palette, and allowing debugger generated output.
*/
int (*con_debug_enter)(struct vc_data *);
/*
* Restore the console to its pre-debug state as closely as possible.
*/
int (*con_debug_leave)(struct vc_data *);
};
extern const struct consw *conswitchp;
extern const struct consw dummy_con; /* dummy console buffer */
extern const struct consw vga_con; /* VGA text console */
extern const struct consw newport_con; /* SGI Newport console */
extern const struct consw prom_con; /* SPARC PROM console */
int con_is_bound(const struct consw *csw);
int do_unregister_con_driver(const struct consw *csw);
int do_take_over_console(const struct consw *sw, int first, int last, int deflt);
void give_up_console(const struct consw *sw);
#ifdef CONFIG_HW_CONSOLE
int con_debug_enter(struct vc_data *vc);
int con_debug_leave(void);
#else
static inline int con_debug_enter(struct vc_data *vc)
{
return 0;
}
static inline int con_debug_leave(void)
{
return 0;
}
#endif
/* scroll */
#define SM_UP (1)
#define SM_DOWN (2)
/* cursor */
#define CM_DRAW (1)
#define CM_ERASE (2)
#define CM_MOVE (3)
/*
* The interface for a console, or any other device that wants to capture
* console messages (printer driver?)
*
* If a console driver is marked CON_BOOT then it will be auto-unregistered
* when the first real console is registered. This is for early-printk drivers.
*/
#define CON_PRINTBUFFER (1)
#define CON_CONSDEV (2) /* Last on the command line */
#define CON_ENABLED (4)
#define CON_BOOT (8)
#define CON_ANYTIME (16) /* Safe to call when cpu is offline */
#define CON_BRL (32) /* Used for a braille device */
#define CON_EXTENDED (64) /* Use the extended output format a la /dev/kmsg */
struct console {
char name[16];
void (*write)(struct console *, const char *, unsigned);
int (*read)(struct console *, char *, unsigned);
struct tty_driver *(*device)(struct console *, int *);
void (*unblank)(void);
int (*setup)(struct console *, char *);
int (*match)(struct console *, char *name, int idx, char *options);
short flags;
short index;
int cflag;
void *data;
struct console *next;
};
/*
* for_each_console() allows you to iterate on each console
*/
#define for_each_console(con) \
for (con = console_drivers; con != NULL; con = con->next)
extern int console_set_on_cmdline;
extern struct console *early_console;
extern int add_preferred_console(char *name, int idx, char *options);
extern void register_console(struct console *);
extern int unregister_console(struct console *);
extern struct console *console_drivers;
extern void console_lock(void);
extern int console_trylock(void);
extern void console_unlock(void);
extern void console_conditional_schedule(void);
extern void console_unblank(void);
extern void console_flush_on_panic(void);
extern struct tty_driver *console_device(int *);
extern void console_stop(struct console *);
extern void console_start(struct console *);
extern int is_console_locked(void);
extern int braille_register_console(struct console *, int index,
char *console_options, char *braille_options);
extern int braille_unregister_console(struct console *);
#ifdef CONFIG_TTY
extern void console_sysfs_notify(void);
#else
static inline void console_sysfs_notify(void)
{ }
#endif
extern bool console_suspend_enabled;
/* Suspend and resume console messages over PM events */
extern void suspend_console(void);
extern void resume_console(void);
int mda_console_init(void);
void prom_con_init(void);
void vcs_make_sysfs(int index);
void vcs_remove_sysfs(int index);
/* Some debug stub to catch some of the obvious races in the VT code */
#if 1
#define WARN_CONSOLE_UNLOCKED() WARN_ON(!is_console_locked() && !oops_in_progress)
#else
#define WARN_CONSOLE_UNLOCKED()
#endif
/* VESA Blanking Levels */
#define VESA_NO_BLANKING 0
#define VESA_VSYNC_SUSPEND 1
#define VESA_HSYNC_SUSPEND 2
#define VESA_POWERDOWN 3
#ifdef CONFIG_VGA_CONSOLE
extern bool vgacon_text_force(void);
#endif
#endif /* _LINUX_CONSOLE_H */
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