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39f610e40e
As Ilya Zykov identified in his patch 'PROBLEM: Race condition in tty buffer's function flush_to_ldisc()', a race condition exists which allows a parallel flush_to_ldisc() to flush and free the tty flip buffers while those buffers are in-use. For example, CPU 0 | CPU 1 | CPU 2 | flush_to_ldisc() | | grab spin lock | tty_buffer_flush() | | flush_to_ldisc() wait for spin lock | | wait for spin lock | if (!test_and_set_bit(TTYP_FLUSHING)) | | while (next flip buffer) | | ... | | drop spin lock | grab spin lock | | if (test_bit(TTYP_FLUSHING)) | | set_bit(TTYP_FLUSHPENDING) | receive_buf() | drop spin lock | | | | grab spin lock | | if (!test_and_set_bit(TTYP_FLUSHING)) | | if (test_bit(TTYP_FLUSHPENDING)) | | __tty_buffer_flush() CPU 2 has just flushed and freed all tty flip buffers while CPU 1 is transferring data from the head flip buffer. The original patch was rejected under the assumption that parallel flush_to_ldisc() was not possible. Because of necessary changes to the workqueue api, work items can execute in parallel on SMP. This patch differs slightly from the original patch by testing for a pending flush _after_ each receive_buf(), since TTYP_FLUSHPENDING can only be set while the lock is dropped around receive_buf(). Reported-by: Ilya Zykov <linux@izyk.ru> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Acked-by: Ilya Zykov <linux@izyk.ru> Cc: Jiri Slaby <jslaby@suse.cz> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
549 lines
14 KiB
C
549 lines
14 KiB
C
/*
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* Tty buffer allocation management
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*/
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#include <linux/types.h>
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#include <linux/errno.h>
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#include <linux/tty.h>
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#include <linux/tty_driver.h>
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#include <linux/tty_flip.h>
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#include <linux/timer.h>
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#include <linux/string.h>
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#include <linux/slab.h>
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#include <linux/sched.h>
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#include <linux/init.h>
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#include <linux/wait.h>
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#include <linux/bitops.h>
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#include <linux/delay.h>
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#include <linux/module.h>
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#include <linux/ratelimit.h>
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/**
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* tty_buffer_free_all - free buffers used by a tty
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* @tty: tty to free from
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*
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* Remove all the buffers pending on a tty whether queued with data
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* or in the free ring. Must be called when the tty is no longer in use
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*
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* Locking: none
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*/
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void tty_buffer_free_all(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *thead;
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while ((thead = buf->head) != NULL) {
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buf->head = thead->next;
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kfree(thead);
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}
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while ((thead = buf->free) != NULL) {
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buf->free = thead->next;
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kfree(thead);
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}
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buf->tail = NULL;
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buf->memory_used = 0;
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}
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/**
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* tty_buffer_alloc - allocate a tty buffer
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* @tty: tty device
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* @size: desired size (characters)
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*
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* Allocate a new tty buffer to hold the desired number of characters.
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* Return NULL if out of memory or the allocation would exceed the
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* per device queue
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*
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* Locking: Caller must hold tty->buf.lock
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*/
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static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
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{
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struct tty_buffer *p;
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if (port->buf.memory_used + size > 65536)
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return NULL;
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p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC);
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if (p == NULL)
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return NULL;
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p->used = 0;
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p->size = size;
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p->next = NULL;
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p->commit = 0;
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p->read = 0;
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p->char_buf_ptr = (char *)(p->data);
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p->flag_buf_ptr = (unsigned char *)p->char_buf_ptr + size;
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port->buf.memory_used += size;
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return p;
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}
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/**
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* tty_buffer_free - free a tty buffer
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* @tty: tty owning the buffer
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* @b: the buffer to free
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*
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* Free a tty buffer, or add it to the free list according to our
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* internal strategy
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*
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* Locking: Caller must hold tty->buf.lock
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*/
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static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
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{
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struct tty_bufhead *buf = &port->buf;
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/* Dumb strategy for now - should keep some stats */
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buf->memory_used -= b->size;
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WARN_ON(buf->memory_used < 0);
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if (b->size >= 512)
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kfree(b);
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else {
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b->next = buf->free;
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buf->free = b;
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}
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}
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/**
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* __tty_buffer_flush - flush full tty buffers
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* @tty: tty to flush
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*
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* flush all the buffers containing receive data. Caller must
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* hold the buffer lock and must have ensured no parallel flush to
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* ldisc is running.
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*
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* Locking: Caller must hold tty->buf.lock
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*/
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static void __tty_buffer_flush(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *thead;
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if (unlikely(buf->head == NULL))
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return;
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while ((thead = buf->head->next) != NULL) {
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tty_buffer_free(port, buf->head);
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buf->head = thead;
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}
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WARN_ON(buf->head != buf->tail);
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buf->head->read = buf->head->commit;
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}
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/**
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* tty_buffer_flush - flush full tty buffers
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* @tty: tty to flush
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*
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* flush all the buffers containing receive data. If the buffer is
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* being processed by flush_to_ldisc then we defer the processing
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* to that function
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*
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* Locking: none
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*/
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void tty_buffer_flush(struct tty_struct *tty)
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{
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struct tty_port *port = tty->port;
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struct tty_bufhead *buf = &port->buf;
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unsigned long flags;
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spin_lock_irqsave(&buf->lock, flags);
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/* If the data is being pushed to the tty layer then we can't
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process it here. Instead set a flag and the flush_to_ldisc
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path will process the flush request before it exits */
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if (test_bit(TTYP_FLUSHING, &port->iflags)) {
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set_bit(TTYP_FLUSHPENDING, &port->iflags);
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spin_unlock_irqrestore(&buf->lock, flags);
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wait_event(tty->read_wait,
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test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
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return;
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} else
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__tty_buffer_flush(port);
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spin_unlock_irqrestore(&buf->lock, flags);
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}
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/**
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* tty_buffer_find - find a free tty buffer
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* @tty: tty owning the buffer
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* @size: characters wanted
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*
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* Locate an existing suitable tty buffer or if we are lacking one then
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* allocate a new one. We round our buffers off in 256 character chunks
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* to get better allocation behaviour.
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*
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* Locking: Caller must hold tty->buf.lock
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*/
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static struct tty_buffer *tty_buffer_find(struct tty_port *port, size_t size)
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{
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struct tty_buffer **tbh = &port->buf.free;
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while ((*tbh) != NULL) {
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struct tty_buffer *t = *tbh;
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if (t->size >= size) {
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*tbh = t->next;
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t->next = NULL;
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t->used = 0;
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t->commit = 0;
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t->read = 0;
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port->buf.memory_used += t->size;
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return t;
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}
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tbh = &((*tbh)->next);
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}
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/* Round the buffer size out */
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size = (size + 0xFF) & ~0xFF;
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return tty_buffer_alloc(port, size);
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/* Should possibly check if this fails for the largest buffer we
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have queued and recycle that ? */
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}
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/**
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* tty_buffer_request_room - grow tty buffer if needed
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* @tty: tty structure
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* @size: size desired
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*
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* Make at least size bytes of linear space available for the tty
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* buffer. If we fail return the size we managed to find.
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*
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* Locking: Takes port->buf.lock
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*/
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int tty_buffer_request_room(struct tty_port *port, size_t size)
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{
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struct tty_bufhead *buf = &port->buf;
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struct tty_buffer *b, *n;
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int left;
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unsigned long flags;
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spin_lock_irqsave(&buf->lock, flags);
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/* OPTIMISATION: We could keep a per tty "zero" sized buffer to
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remove this conditional if its worth it. This would be invisible
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to the callers */
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b = buf->tail;
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if (b != NULL)
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left = b->size - b->used;
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else
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left = 0;
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if (left < size) {
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/* This is the slow path - looking for new buffers to use */
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if ((n = tty_buffer_find(port, size)) != NULL) {
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if (b != NULL) {
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b->next = n;
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b->commit = b->used;
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} else
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buf->head = n;
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buf->tail = n;
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} else
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size = left;
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}
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spin_unlock_irqrestore(&buf->lock, flags);
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return size;
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}
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EXPORT_SYMBOL_GPL(tty_buffer_request_room);
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/**
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* tty_insert_flip_string_fixed_flag - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flag: flag value for each character
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. All the characters
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* passed are marked with the supplied flag. Returns the number added.
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*
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* Locking: Called functions may take port->buf.lock
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*/
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int tty_insert_flip_string_fixed_flag(struct tty_port *port,
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const unsigned char *chars, char flag, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int space = tty_buffer_request_room(port, goal);
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struct tty_buffer *tb = port->buf.tail;
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/* If there is no space then tb may be NULL */
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if (unlikely(space == 0)) {
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break;
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}
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memcpy(tb->char_buf_ptr + tb->used, chars, space);
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memset(tb->flag_buf_ptr + tb->used, flag, space);
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tb->used += space;
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copied += space;
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chars += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag);
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/**
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* tty_insert_flip_string_flags - Add characters to the tty buffer
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* @port: tty port
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* @chars: characters
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* @flags: flag bytes
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* @size: size
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*
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* Queue a series of bytes to the tty buffering. For each character
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* the flags array indicates the status of the character. Returns the
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* number added.
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*
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* Locking: Called functions may take port->buf.lock
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*/
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int tty_insert_flip_string_flags(struct tty_port *port,
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const unsigned char *chars, const char *flags, size_t size)
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{
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int copied = 0;
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do {
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int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
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int space = tty_buffer_request_room(port, goal);
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struct tty_buffer *tb = port->buf.tail;
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/* If there is no space then tb may be NULL */
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if (unlikely(space == 0)) {
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break;
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}
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memcpy(tb->char_buf_ptr + tb->used, chars, space);
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memcpy(tb->flag_buf_ptr + tb->used, flags, space);
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tb->used += space;
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copied += space;
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chars += space;
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flags += space;
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/* There is a small chance that we need to split the data over
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several buffers. If this is the case we must loop */
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} while (unlikely(size > copied));
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return copied;
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}
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EXPORT_SYMBOL(tty_insert_flip_string_flags);
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/**
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* tty_schedule_flip - push characters to ldisc
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* @port: tty port to push from
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*
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* Takes any pending buffers and transfers their ownership to the
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* ldisc side of the queue. It then schedules those characters for
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* processing by the line discipline.
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* Note that this function can only be used when the low_latency flag
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* is unset. Otherwise the workqueue won't be flushed.
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*
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* Locking: Takes port->buf.lock
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*/
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void tty_schedule_flip(struct tty_port *port)
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{
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struct tty_bufhead *buf = &port->buf;
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unsigned long flags;
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WARN_ON(port->low_latency);
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spin_lock_irqsave(&buf->lock, flags);
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if (buf->tail != NULL)
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buf->tail->commit = buf->tail->used;
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spin_unlock_irqrestore(&buf->lock, flags);
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schedule_work(&buf->work);
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}
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EXPORT_SYMBOL(tty_schedule_flip);
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/**
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* tty_prepare_flip_string - make room for characters
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* @port: tty port
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* @chars: return pointer for character write area
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* @size: desired size
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*
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* Prepare a block of space in the buffer for data. Returns the length
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* available and buffer pointer to the space which is now allocated and
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* accounted for as ready for normal characters. This is used for drivers
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* that need their own block copy routines into the buffer. There is no
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* guarantee the buffer is a DMA target!
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*
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* Locking: May call functions taking port->buf.lock
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*/
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int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars,
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size_t size)
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{
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int space = tty_buffer_request_room(port, size);
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if (likely(space)) {
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struct tty_buffer *tb = port->buf.tail;
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*chars = tb->char_buf_ptr + tb->used;
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memset(tb->flag_buf_ptr + tb->used, TTY_NORMAL, space);
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tb->used += space;
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}
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return space;
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}
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EXPORT_SYMBOL_GPL(tty_prepare_flip_string);
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/**
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* tty_prepare_flip_string_flags - make room for characters
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* @port: tty port
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* @chars: return pointer for character write area
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* @flags: return pointer for status flag write area
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* @size: desired size
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*
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* Prepare a block of space in the buffer for data. Returns the length
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* available and buffer pointer to the space which is now allocated and
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* accounted for as ready for characters. This is used for drivers
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* that need their own block copy routines into the buffer. There is no
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* guarantee the buffer is a DMA target!
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*
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* Locking: May call functions taking port->buf.lock
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*/
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int tty_prepare_flip_string_flags(struct tty_port *port,
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unsigned char **chars, char **flags, size_t size)
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{
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int space = tty_buffer_request_room(port, size);
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if (likely(space)) {
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struct tty_buffer *tb = port->buf.tail;
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*chars = tb->char_buf_ptr + tb->used;
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*flags = tb->flag_buf_ptr + tb->used;
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tb->used += space;
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}
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return space;
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}
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EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
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/**
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* flush_to_ldisc
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* @work: tty structure passed from work queue.
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*
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* This routine is called out of the software interrupt to flush data
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* from the buffer chain to the line discipline.
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*
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* Locking: holds tty->buf.lock to guard buffer list. Drops the lock
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* while invoking the line discipline receive_buf method. The
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* receive_buf method is single threaded for each tty instance.
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*/
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static void flush_to_ldisc(struct work_struct *work)
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{
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struct tty_port *port = container_of(work, struct tty_port, buf.work);
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struct tty_bufhead *buf = &port->buf;
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struct tty_struct *tty;
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unsigned long flags;
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struct tty_ldisc *disc;
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tty = port->itty;
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if (tty == NULL)
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return;
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disc = tty_ldisc_ref(tty);
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if (disc == NULL) /* !TTY_LDISC */
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return;
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spin_lock_irqsave(&buf->lock, flags);
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if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
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struct tty_buffer *head;
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while ((head = buf->head) != NULL) {
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int count;
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char *char_buf;
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unsigned char *flag_buf;
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count = head->commit - head->read;
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if (!count) {
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if (head->next == NULL)
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break;
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buf->head = head->next;
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tty_buffer_free(port, head);
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continue;
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}
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if (!tty->receive_room)
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break;
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if (count > tty->receive_room)
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count = tty->receive_room;
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char_buf = head->char_buf_ptr + head->read;
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flag_buf = head->flag_buf_ptr + head->read;
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head->read += count;
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spin_unlock_irqrestore(&buf->lock, flags);
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disc->ops->receive_buf(tty, char_buf,
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flag_buf, count);
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spin_lock_irqsave(&buf->lock, flags);
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/* Ldisc or user is trying to flush the buffers.
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We may have a deferred request to flush the
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input buffer, if so pull the chain under the lock
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and empty the queue */
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if (test_bit(TTYP_FLUSHPENDING, &port->iflags)) {
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__tty_buffer_flush(port);
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clear_bit(TTYP_FLUSHPENDING, &port->iflags);
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wake_up(&tty->read_wait);
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break;
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}
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}
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clear_bit(TTYP_FLUSHING, &port->iflags);
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}
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spin_unlock_irqrestore(&buf->lock, flags);
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tty_ldisc_deref(disc);
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}
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/**
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* tty_flush_to_ldisc
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* @tty: tty to push
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*
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* Push the terminal flip buffers to the line discipline.
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*
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* Must not be called from IRQ context.
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*/
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void tty_flush_to_ldisc(struct tty_struct *tty)
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{
|
|
if (!tty->port->low_latency)
|
|
flush_work(&tty->port->buf.work);
|
|
}
|
|
|
|
/**
|
|
* tty_flip_buffer_push - terminal
|
|
* @port: tty port to push
|
|
*
|
|
* Queue a push of the terminal flip buffers to the line discipline. This
|
|
* function must not be called from IRQ context if port->low_latency is
|
|
* set.
|
|
*
|
|
* In the event of the queue being busy for flipping the work will be
|
|
* held off and retried later.
|
|
*
|
|
* Locking: tty buffer lock. Driver locks in low latency mode.
|
|
*/
|
|
|
|
void tty_flip_buffer_push(struct tty_port *port)
|
|
{
|
|
struct tty_bufhead *buf = &port->buf;
|
|
unsigned long flags;
|
|
|
|
spin_lock_irqsave(&buf->lock, flags);
|
|
if (buf->tail != NULL)
|
|
buf->tail->commit = buf->tail->used;
|
|
spin_unlock_irqrestore(&buf->lock, flags);
|
|
|
|
if (port->low_latency)
|
|
flush_to_ldisc(&buf->work);
|
|
else
|
|
schedule_work(&buf->work);
|
|
}
|
|
EXPORT_SYMBOL(tty_flip_buffer_push);
|
|
|
|
/**
|
|
* tty_buffer_init - prepare a tty buffer structure
|
|
* @tty: tty to initialise
|
|
*
|
|
* Set up the initial state of the buffer management for a tty device.
|
|
* Must be called before the other tty buffer functions are used.
|
|
*
|
|
* Locking: none
|
|
*/
|
|
|
|
void tty_buffer_init(struct tty_port *port)
|
|
{
|
|
struct tty_bufhead *buf = &port->buf;
|
|
|
|
spin_lock_init(&buf->lock);
|
|
buf->head = NULL;
|
|
buf->tail = NULL;
|
|
buf->free = NULL;
|
|
buf->memory_used = 0;
|
|
INIT_WORK(&buf->work, flush_to_ldisc);
|
|
}
|
|
|