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Commit 7bfe0b71 authored by Peter Hurley's avatar Peter Hurley Committed by Greg Kroah-Hartman
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tty: Track flip buffer memory limit atomically 



Lockless flip buffers require atomically updating the bytes-in-use
watermark.

The pty driver also peeks at the watermark value to limit
memory consumption to a much lower value than the default; query
the watermark with new fn, tty_buffer_space_avail().

Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 7391ee16

drivers/tty/pty.c

+3 −7
Original line number Diff line number Diff line
@@ -89,17 +89,13 @@ static void pty_unthrottle(struct tty_struct *tty) 
 *	pty_space	-	report space left for writing

 *	@to: tty we are writing into

 *

 *	The tty buffers allow 64K but we sneak a peak and clip at 8K this

 *	allows a lot of overspill room for echo and other fun messes to

 *	be handled properly

 *	Limit the buffer space used by ptys to 8k.

 */



static int pty_space(struct tty_struct *to)

{

	int n = 8192 - to->port->buf.memory_used;

	if (n < 0)

		return 0;

	return n;

	int n = tty_buffer_space_avail(to->port);

	return min(n, 8192);

}



/**

drivers/tty/tty_buffer.c

+31 −6
Original line number Diff line number Diff line
@@ -22,6 +22,31 @@ 
#define MIN_TTYB_SIZE	256

#define TTYB_ALIGN_MASK	255



/*

 * Byte threshold to limit memory consumption for flip buffers.

 * The actual memory limit is > 2x this amount.

 */

#define TTYB_MEM_LIMIT	65536





/**

 *	tty_buffer_space_avail	-	return unused buffer space

 *	@port - tty_port owning the flip buffer

 *

 *	Returns the # of bytes which can be written by the driver without

 *	reaching the buffer limit.

 *

 *	Note: this does not guarantee that memory is available to write

 *	the returned # of bytes (use tty_prepare_flip_string_xxx() to

 *	pre-allocate if memory guarantee is required).

 */



int tty_buffer_space_avail(struct tty_port *port)

{

	int space = TTYB_MEM_LIMIT - atomic_read(&port->buf.memory_used);

	return max(space, 0);

}



static void tty_buffer_reset(struct tty_buffer *p, size_t size)

{

	p->used = 0;
@@ -59,7 +84,8 @@ void tty_buffer_free_all(struct tty_port *port) 
	tty_buffer_reset(&buf->sentinel, 0);

	buf->head = &buf->sentinel;

	buf->tail = &buf->sentinel;

	buf->memory_used = 0;



	atomic_set(&buf->memory_used, 0);

}



/**
@@ -92,7 +118,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) 


	/* Should possibly check if this fails for the largest buffer we

	   have queued and recycle that ? */

	if (port->buf.memory_used + size > 65536)

	if (atomic_read(&port->buf.memory_used) > TTYB_MEM_LIMIT)

		return NULL;

	p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);

	if (p == NULL)
@@ -100,7 +126,7 @@ static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) 


found:

	tty_buffer_reset(p, size);

	port->buf.memory_used += size;

	atomic_add(size, &port->buf.memory_used);

	return p;

}
@@ -118,8 +144,7 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b) 
	struct tty_bufhead *buf = &port->buf;



	/* Dumb strategy for now - should keep some stats */

	buf->memory_used -= b->size;

	WARN_ON(buf->memory_used < 0);

	WARN_ON(atomic_sub_return(b->size, &buf->memory_used) < 0);



	if (b->size > MIN_TTYB_SIZE)

		kfree(b);
@@ -525,7 +550,7 @@ void tty_buffer_init(struct tty_port *port) 
	buf->head = &buf->sentinel;

	buf->tail = &buf->sentinel;

	init_llist_head(&buf->free);

	buf->memory_used = 0;

	atomic_set(&buf->memory_used, 0);

	INIT_WORK(&buf->work, flush_to_ldisc);

}

include/linux/tty.h

+1 −2
Original line number Diff line number Diff line
@@ -71,8 +71,7 @@ struct tty_bufhead { 
	struct tty_buffer *head;	/* Queue head */

	struct tty_buffer *tail;	/* Active buffer */

	struct llist_head free;		/* Free queue head */

	int memory_used;		/* Buffer space used excluding

								free queue */

	atomic_t	   memory_used; /* In-use buffers excluding free list */

};

/*

 * When a break, frame error, or parity error happens, these codes are

include/linux/tty_flip.h

+1 −0
Original line number Diff line number Diff line 
#ifndef _LINUX_TTY_FLIP_H

#define _LINUX_TTY_FLIP_H



extern int tty_buffer_space_avail(struct tty_port *port);

extern int tty_buffer_request_room(struct tty_port *port, size_t size);

extern int tty_insert_flip_string_flags(struct tty_port *port,

		const unsigned char *chars, const char *flags, size_t size);