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authorAlan Cox <alan@redhat.com>2007-07-15 23:39:43 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-07-16 09:05:41 -0700
commit9c1729db3e6d738f872bcb090212af00473bf666 (patch)
treebe68b99784607953fb50d9330d34c2728215be57 /drivers
parentc9c64155f5a81b4b41e98f9fb9c464a565c1bf72 (diff)
downloadlinux-linaro-stable-9c1729db3e6d738f872bcb090212af00473bf666.tar.gz
Prevent an O_NDELAY writer from blocking when a tty write is blocked by the tty atomic writer mutex
Without this a tty write could block if a previous blocking tty write was in progress on the same tty and blocked by a line discipline or hardware event. Originally found and reported by Dave Johnson. Signed-off-by: Alan Cox <alan@redhat.com> Acked-by: Dave Johnson <djohnson+linux-kernel@sw.starentnetworks.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/char/n_hdlc.c9
-rw-r--r--drivers/char/n_tty.c3
-rw-r--r--drivers/char/tty_io.c40
-rw-r--r--drivers/char/tty_ioctl.c4
4 files changed, 37 insertions, 19 deletions
diff --git a/drivers/char/n_hdlc.c b/drivers/char/n_hdlc.c
index 337a87f86a3b..37f7d3403040 100644
--- a/drivers/char/n_hdlc.c
+++ b/drivers/char/n_hdlc.c
@@ -780,13 +780,14 @@ static unsigned int n_hdlc_tty_poll(struct tty_struct *tty, struct file *filp,
poll_wait(filp, &tty->write_wait, wait);
/* set bits for operations that won't block */
- if(n_hdlc->rx_buf_list.head)
+ if (n_hdlc->rx_buf_list.head)
mask |= POLLIN | POLLRDNORM; /* readable */
if (test_bit(TTY_OTHER_CLOSED, &tty->flags))
mask |= POLLHUP;
- if(tty_hung_up_p(filp))
+ if (tty_hung_up_p(filp))
mask |= POLLHUP;
- if(n_hdlc->tx_free_buf_list.head)
+ if (!tty_is_writelocked(tty) &&
+ n_hdlc->tx_free_buf_list.head)
mask |= POLLOUT | POLLWRNORM; /* writable */
}
return mask;
@@ -861,7 +862,7 @@ static void n_hdlc_buf_put(struct n_hdlc_buf_list *list,
spin_lock_irqsave(&list->spinlock,flags);
buf->link=NULL;
- if(list->tail)
+ if (list->tail)
list->tail->link = buf;
else
list->head = buf;
diff --git a/drivers/char/n_tty.c b/drivers/char/n_tty.c
index 154f42203b05..371631f4bfb9 100644
--- a/drivers/char/n_tty.c
+++ b/drivers/char/n_tty.c
@@ -1538,7 +1538,8 @@ static unsigned int normal_poll(struct tty_struct * tty, struct file * file, pol
else
tty->minimum_to_wake = 1;
}
- if (tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
+ if (!tty_is_writelocked(tty) &&
+ tty->driver->chars_in_buffer(tty) < WAKEUP_CHARS &&
tty->driver->write_room(tty) > 0)
mask |= POLLOUT | POLLWRNORM;
return mask;
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index a96f26a63fa2..a37e6330db8a 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1726,6 +1726,23 @@ static ssize_t tty_read(struct file * file, char __user * buf, size_t count,
return i;
}
+void tty_write_unlock(struct tty_struct *tty)
+{
+ mutex_unlock(&tty->atomic_write_lock);
+ wake_up_interruptible(&tty->write_wait);
+}
+
+int tty_write_lock(struct tty_struct *tty, int ndelay)
+{
+ if (!mutex_trylock(&tty->atomic_write_lock)) {
+ if (ndelay)
+ return -EAGAIN;
+ if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ return -ERESTARTSYS;
+ }
+ return 0;
+}
+
/*
* Split writes up in sane blocksizes to avoid
* denial-of-service type attacks
@@ -1737,13 +1754,12 @@ static inline ssize_t do_tty_write(
const char __user *buf,
size_t count)
{
- ssize_t ret = 0, written = 0;
+ ssize_t ret, written = 0;
unsigned int chunk;
- /* FIXME: O_NDELAY ... */
- if (mutex_lock_interruptible(&tty->atomic_write_lock)) {
- return -ERESTARTSYS;
- }
+ ret = tty_write_lock(tty, file->f_flags & O_NDELAY);
+ if (ret < 0)
+ return ret;
/*
* We chunk up writes into a temporary buffer. This
@@ -1776,8 +1792,8 @@ static inline ssize_t do_tty_write(
buf = kmalloc(chunk, GFP_KERNEL);
if (!buf) {
- mutex_unlock(&tty->atomic_write_lock);
- return -ENOMEM;
+ ret = -ENOMEM;
+ goto out;
}
kfree(tty->write_buf);
tty->write_cnt = chunk;
@@ -1812,7 +1828,8 @@ static inline ssize_t do_tty_write(
inode->i_mtime = current_fs_time(inode->i_sb);
ret = written;
}
- mutex_unlock(&tty->atomic_write_lock);
+out:
+ tty_write_unlock(tty);
return ret;
}
@@ -3163,14 +3180,13 @@ static int tiocsetd(struct tty_struct *tty, int __user *p)
static int send_break(struct tty_struct *tty, unsigned int duration)
{
- if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ if (tty_write_lock(tty, 0) < 0)
return -EINTR;
tty->driver->break_ctl(tty, -1);
- if (!signal_pending(current)) {
+ if (!signal_pending(current))
msleep_interruptible(duration);
- }
tty->driver->break_ctl(tty, 0);
- mutex_unlock(&tty->atomic_write_lock);
+ tty_write_unlock(tty);
if (signal_pending(current))
return -EINTR;
return 0;
diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
index fd471cb3338f..918e24c885f1 100644
--- a/drivers/char/tty_ioctl.c
+++ b/drivers/char/tty_ioctl.c
@@ -667,7 +667,7 @@ static int send_prio_char(struct tty_struct *tty, char ch)
return 0;
}
- if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ if (tty_write_lock(tty, 0) < 0)
return -ERESTARTSYS;
if (was_stopped)
@@ -675,7 +675,7 @@ static int send_prio_char(struct tty_struct *tty, char ch)
tty->driver->write(tty, &ch, 1);
if (was_stopped)
stop_tty(tty);
- mutex_unlock(&tty->atomic_write_lock);
+ tty_write_unlock(tty);
return 0;
}