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linux-next/include/linux/tty_ldisc.h
Huang Shijie 879eb9c3f9 tty_ldisc: add more limits to the @write_wakeup
In the uart_handle_cts_change(), uart_write_wakeup() is called after
we call @uart_port->ops->start_tx().

The Documentation/serial/driver tells us:
-----------------------------------------------
  start_tx(port)
	Start transmitting characters.

	Locking: port->lock taken.
	Interrupts: locally disabled.
-----------------------------------------------

So when the uart_write_wakeup() is called, the port->lock is taken by
the upper. See the following callstack:

	|_ uart_write_wakeup
	   |_ tty_wakeup
	      |_ ld->ops->write_wakeup

With the port->lock held, we call the @write_wakeup. Some implemetation of
the @write_wakeup does not notice that the port->lock is held, and it still
tries to send data with uart_write() which will try to grab the prot->lock.
A dead lock occurs, see the following log caught in the Bluetooth by uart:

--------------------------------------------------------------------
BUG: spinlock lockup suspected on CPU#0, swapper/0/0
 lock: 0xdc3f4410, .magic: dead4ead, .owner: swapper/0/0, .owner_cpu: 0
CPU: 0 PID: 0 Comm: swapper/0 Tainted: G        W    3.10.17-16839-ge4a1bef #1320
[<80014cbc>] (unwind_backtrace+0x0/0x138) from [<8001251c>] (show_stack+0x10/0x14)
[<8001251c>] (show_stack+0x10/0x14) from [<802816ac>] (do_raw_spin_lock+0x108/0x184)
[<802816ac>] (do_raw_spin_lock+0x108/0x184) from [<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60)
[<806a22b0>] (_raw_spin_lock_irqsave+0x54/0x60) from [<802f5754>] (uart_write+0x38/0xe0)
[<802f5754>] (uart_write+0x38/0xe0) from [<80455270>] (hci_uart_tx_wakeup+0xa4/0x168)
[<80455270>] (hci_uart_tx_wakeup+0xa4/0x168) from [<802dab18>] (tty_wakeup+0x50/0x5c)
[<802dab18>] (tty_wakeup+0x50/0x5c) from [<802f81a4>] (imx_rtsint+0x50/0x80)
[<802f81a4>] (imx_rtsint+0x50/0x80) from [<802f88f4>] (imx_int+0x158/0x17c)
[<802f88f4>] (imx_int+0x158/0x17c) from [<8007abe0>] (handle_irq_event_percpu+0x50/0x194)
[<8007abe0>] (handle_irq_event_percpu+0x50/0x194) from [<8007ad60>] (handle_irq_event+0x3c/0x5c)
--------------------------------------------------------------------

This patch adds more limits to the @write_wakeup, the one who wants to
implemet the @write_wakeup should follow the limits which avoid the deadlock.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2014-04-24 16:16:33 -07:00

234 lines
8.1 KiB
C

#ifndef _LINUX_TTY_LDISC_H
#define _LINUX_TTY_LDISC_H
/*
* This structure defines the interface between the tty line discipline
* implementation and the tty routines. The following routines can be
* defined; unless noted otherwise, they are optional, and can be
* filled in with a null pointer.
*
* int (*open)(struct tty_struct *);
*
* This function is called when the line discipline is associated
* with the tty. The line discipline can use this as an
* opportunity to initialize any state needed by the ldisc routines.
*
* void (*close)(struct tty_struct *);
*
* This function is called when the line discipline is being
* shutdown, either because the tty is being closed or because
* the tty is being changed to use a new line discipline
*
* void (*flush_buffer)(struct tty_struct *tty);
*
* This function instructs the line discipline to clear its
* buffers of any input characters it may have queued to be
* delivered to the user mode process.
*
* ssize_t (*chars_in_buffer)(struct tty_struct *tty);
*
* This function returns the number of input characters the line
* discipline may have queued up to be delivered to the user mode
* process.
*
* ssize_t (*read)(struct tty_struct * tty, struct file * file,
* unsigned char * buf, size_t nr);
*
* This function is called when the user requests to read from
* the tty. The line discipline will return whatever characters
* it has buffered up for the user. If this function is not
* defined, the user will receive an EIO error.
*
* ssize_t (*write)(struct tty_struct * tty, struct file * file,
* const unsigned char * buf, size_t nr);
*
* This function is called when the user requests to write to the
* tty. The line discipline will deliver the characters to the
* low-level tty device for transmission, optionally performing
* some processing on the characters first. If this function is
* not defined, the user will receive an EIO error.
*
* int (*ioctl)(struct tty_struct * tty, struct file * file,
* unsigned int cmd, unsigned long arg);
*
* This function is called when the user requests an ioctl which
* is not handled by the tty layer or the low-level tty driver.
* It is intended for ioctls which affect line discpline
* operation. Note that the search order for ioctls is (1) tty
* layer, (2) tty low-level driver, (3) line discpline. So a
* low-level driver can "grab" an ioctl request before the line
* discpline has a chance to see it.
*
* long (*compat_ioctl)(struct tty_struct * tty, struct file * file,
* unsigned int cmd, unsigned long arg);
*
* Process ioctl calls from 32-bit process on 64-bit system
*
* void (*set_termios)(struct tty_struct *tty, struct ktermios * old);
*
* This function notifies the line discpline that a change has
* been made to the termios structure.
*
* int (*poll)(struct tty_struct * tty, struct file * file,
* poll_table *wait);
*
* This function is called when a user attempts to select/poll on a
* tty device. It is solely the responsibility of the line
* discipline to handle poll requests.
*
* void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
* char *fp, int count);
*
* This function is called by the low-level tty driver to send
* characters received by the hardware to the line discpline for
* processing. <cp> is a pointer to the buffer of input
* character received by the device. <fp> is a pointer to a
* pointer of flag bytes which indicate whether a character was
* received with a parity error, etc. <fp> may be NULL to indicate
* all data received is TTY_NORMAL.
*
* void (*write_wakeup)(struct tty_struct *);
*
* This function is called by the low-level tty driver to signal
* that line discpline should try to send more characters to the
* low-level driver for transmission. If the line discpline does
* not have any more data to send, it can just return. If the line
* discipline does have some data to send, please arise a tasklet
* or workqueue to do the real data transfer. Do not send data in
* this hook, it may leads to a deadlock.
*
* int (*hangup)(struct tty_struct *)
*
* Called on a hangup. Tells the discipline that it should
* cease I/O to the tty driver. Can sleep. The driver should
* seek to perform this action quickly but should wait until
* any pending driver I/O is completed.
*
* void (*fasync)(struct tty_struct *, int on)
*
* Notify line discipline when signal-driven I/O is enabled or
* disabled.
*
* void (*dcd_change)(struct tty_struct *tty, unsigned int status)
*
* Tells the discipline that the DCD pin has changed its status.
* Used exclusively by the N_PPS (Pulse-Per-Second) line discipline.
*
* int (*receive_buf2)(struct tty_struct *, const unsigned char *cp,
* char *fp, int count);
*
* This function is called by the low-level tty driver to send
* characters received by the hardware to the line discpline for
* processing. <cp> is a pointer to the buffer of input
* character received by the device. <fp> is a pointer to a
* pointer of flag bytes which indicate whether a character was
* received with a parity error, etc. <fp> may be NULL to indicate
* all data received is TTY_NORMAL.
* If assigned, prefer this function for automatic flow control.
*/
#include <linux/fs.h>
#include <linux/wait.h>
/*
* the semaphore definition
*/
struct ld_semaphore {
long count;
raw_spinlock_t wait_lock;
unsigned int wait_readers;
struct list_head read_wait;
struct list_head write_wait;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
};
extern void __init_ldsem(struct ld_semaphore *sem, const char *name,
struct lock_class_key *key);
#define init_ldsem(sem) \
do { \
static struct lock_class_key __key; \
\
__init_ldsem((sem), #sem, &__key); \
} while (0)
extern int ldsem_down_read(struct ld_semaphore *sem, long timeout);
extern int ldsem_down_read_trylock(struct ld_semaphore *sem);
extern int ldsem_down_write(struct ld_semaphore *sem, long timeout);
extern int ldsem_down_write_trylock(struct ld_semaphore *sem);
extern void ldsem_up_read(struct ld_semaphore *sem);
extern void ldsem_up_write(struct ld_semaphore *sem);
#ifdef CONFIG_DEBUG_LOCK_ALLOC
extern int ldsem_down_read_nested(struct ld_semaphore *sem, int subclass,
long timeout);
extern int ldsem_down_write_nested(struct ld_semaphore *sem, int subclass,
long timeout);
#else
# define ldsem_down_read_nested(sem, subclass, timeout) \
ldsem_down_read(sem, timeout)
# define ldsem_down_write_nested(sem, subclass, timeout) \
ldsem_down_write(sem, timeout)
#endif
struct tty_ldisc_ops {
int magic;
char *name;
int num;
int flags;
/*
* The following routines are called from above.
*/
int (*open)(struct tty_struct *);
void (*close)(struct tty_struct *);
void (*flush_buffer)(struct tty_struct *tty);
ssize_t (*chars_in_buffer)(struct tty_struct *tty);
ssize_t (*read)(struct tty_struct *tty, struct file *file,
unsigned char __user *buf, size_t nr);
ssize_t (*write)(struct tty_struct *tty, struct file *file,
const unsigned char *buf, size_t nr);
int (*ioctl)(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg);
long (*compat_ioctl)(struct tty_struct *tty, struct file *file,
unsigned int cmd, unsigned long arg);
void (*set_termios)(struct tty_struct *tty, struct ktermios *old);
unsigned int (*poll)(struct tty_struct *, struct file *,
struct poll_table_struct *);
int (*hangup)(struct tty_struct *tty);
/*
* The following routines are called from below.
*/
void (*receive_buf)(struct tty_struct *, const unsigned char *cp,
char *fp, int count);
void (*write_wakeup)(struct tty_struct *);
void (*dcd_change)(struct tty_struct *, unsigned int);
void (*fasync)(struct tty_struct *tty, int on);
int (*receive_buf2)(struct tty_struct *, const unsigned char *cp,
char *fp, int count);
struct module *owner;
int refcount;
};
struct tty_ldisc {
struct tty_ldisc_ops *ops;
struct tty_struct *tty;
};
#define TTY_LDISC_MAGIC 0x5403
#define LDISC_FLAG_DEFINED 0x00000001
#define MODULE_ALIAS_LDISC(ldisc) \
MODULE_ALIAS("tty-ldisc-" __stringify(ldisc))
#endif /* _LINUX_TTY_LDISC_H */