tty: Ensure single-threaded flip buffer consumer with mutex

The buffer work may race with parallel tty_buffer_flush. Use a
mutex to guarantee exclusive modify access to the head flip
buffer.

Remove the unneeded spin lock.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/dgrp/dgrp_tty.c b/drivers/staging/dgrp/dgrp_tty.c
index 654f601..0d52de3 100644 (file)
--- a/drivers/staging/dgrp/dgrp_tty.c
+++ b/drivers/staging/dgrp/dgrp_tty.c
@@ -1120,7 +1120,9 @@ static void dgrp_tty_close(struct tty_struct *tty, struct file *file)
                                if (!sent_printer_offstr)
                                        dgrp_tty_flush_buffer(tty);
 
+                               spin_unlock_irqrestore(&nd->nd_lock, lock_flags);
                                tty_ldisc_flush(tty);
+                               spin_lock_irqsave(&nd->nd_lock, lock_flags);
                                break;
                }
 

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 685757c..c3c606c 100644 (file)
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -157,8 +157,6 @@ static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b)
  *     flush all the buffers containing receive data. Caller must
  *     hold the buffer lock and must have ensured no parallel flush to
  *     ldisc is running.
- *
- *     Locking: Caller must hold tty->buf.lock
  */
 
 static void __tty_buffer_flush(struct tty_port *port)
@@ -182,29 +180,29 @@ static void __tty_buffer_flush(struct tty_port *port)
  *     being processed by flush_to_ldisc then we defer the processing
  *     to that function
  *
- *     Locking: none
+ *     Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *              'consumer'
  */
 
 void tty_buffer_flush(struct tty_struct *tty)
 {
        struct tty_port *port = tty->port;
        struct tty_bufhead *buf = &port->buf;
-       unsigned long flags;
-
-       spin_lock_irqsave(&buf->lock, flags);
 
+       mutex_lock(&buf->flush_mutex);
        /* If the data is being pushed to the tty layer then we can't
           process it here. Instead set a flag and the flush_to_ldisc
           path will process the flush request before it exits */
        if (test_bit(TTYP_FLUSHING, &port->iflags)) {
                set_bit(TTYP_FLUSHPENDING, &port->iflags);
-               spin_unlock_irqrestore(&buf->lock, flags);
+               mutex_unlock(&buf->flush_mutex);
                wait_event(tty->read_wait,
                                test_bit(TTYP_FLUSHPENDING, &port->iflags) == 0);
                return;
-       } else
-               __tty_buffer_flush(port);
-       spin_unlock_irqrestore(&buf->lock, flags);
+       }
+
+       __tty_buffer_flush(port);
+       mutex_unlock(&buf->flush_mutex);
 }
 
 /**
@@ -408,9 +406,10 @@ receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count)
  *     This routine is called out of the software interrupt to flush data
  *     from the buffer chain to the line discipline.
  *
- *     Locking: holds tty->buf.lock to guard buffer list. Drops the lock
- *     while invoking the line discipline receive_buf method. The
- *     receive_buf method is single threaded for each tty instance.
+ *     The receive_buf method is single threaded for each tty instance.
+ *
+ *     Locking: takes flush_mutex to ensure single-threaded flip buffer
+ *              'consumer'
  */
 
 static void flush_to_ldisc(struct work_struct *work)
@@ -418,7 +417,6 @@ static void flush_to_ldisc(struct work_struct *work)
        struct tty_port *port = container_of(work, struct tty_port, buf.work);
        struct tty_bufhead *buf = &port->buf;
        struct tty_struct *tty;
-       unsigned long   flags;
        struct tty_ldisc *disc;
 
        tty = port->itty;
@@ -429,7 +427,7 @@ static void flush_to_ldisc(struct work_struct *work)
        if (disc == NULL)
                return;
 
-       spin_lock_irqsave(&buf->lock, flags);
+       mutex_lock(&buf->flush_mutex);
 
        if (!test_and_set_bit(TTYP_FLUSHING, &port->iflags)) {
                while (1) {
@@ -444,11 +442,13 @@ static void flush_to_ldisc(struct work_struct *work)
                                tty_buffer_free(port, head);
                                continue;
                        }
-                       spin_unlock_irqrestore(&buf->lock, flags);
+
+                       mutex_unlock(&buf->flush_mutex);
 
                        count = receive_buf(tty, head, count);
 
-                       spin_lock_irqsave(&buf->lock, flags);
+                       mutex_lock(&buf->flush_mutex);
+
                        /* Ldisc or user is trying to flush the buffers.
                           We may have a deferred request to flush the
                           input buffer, if so pull the chain under the lock
@@ -464,7 +464,7 @@ static void flush_to_ldisc(struct work_struct *work)
                clear_bit(TTYP_FLUSHING, &port->iflags);
        }
 
-       spin_unlock_irqrestore(&buf->lock, flags);
+       mutex_unlock(&buf->flush_mutex);
 
        tty_ldisc_deref(disc);
 }
@@ -514,15 +514,13 @@ EXPORT_SYMBOL(tty_flip_buffer_push);
  *
  *     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);
+       mutex_init(&buf->flush_mutex);
        tty_buffer_reset(&buf->sentinel, 0);
        buf->head = &buf->sentinel;
        buf->tail = &buf->sentinel;

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 7c12454..1c8fef0 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -66,7 +66,7 @@ static inline char *flag_buf_ptr(struct tty_buffer *b, int ofs)
 
 struct tty_bufhead {
        struct work_struct work;
-       spinlock_t lock;
+       struct mutex flush_mutex;
        struct tty_buffer sentinel;
        struct tty_buffer *head;        /* Queue head */
        struct tty_buffer *tail;        /* Active buffer */