The patch titled
Prevent an O_NDELAY writer from blocking when a tty write is blocked by
has been added to the -mm tree. Its filename is
prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: Prevent an O_NDELAY writer from blocking when a tty write is blocked by
From: Alan Cox <alan@xxxxxxxxxx>
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@xxxxxxxxxx>
Acked-by: Dave Johnson <djohnson+linux-kernel@xxxxxxxxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/n_hdlc.c | 9 ++++----
drivers/char/n_tty.c | 3 +-
drivers/char/tty_io.c | 40 +++++++++++++++++++++++++------------
drivers/char/tty_ioctl.c | 4 +--
include/linux/tty.h | 6 +++++
5 files changed, 43 insertions(+), 19 deletions(-)
diff -puN drivers/char/n_hdlc.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by drivers/char/n_hdlc.c
--- a/drivers/char/n_hdlc.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by
+++ a/drivers/char/n_hdlc.c
@@ -780,13 +780,14 @@ static unsigned int n_hdlc_tty_poll(stru
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
spin_lock_irqsave(&list->spinlock,flags);
buf->link=NULL;
- if(list->tail)
+ if (list->tail)
list->tail->link = buf;
else
list->head = buf;
diff -puN drivers/char/n_tty.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by drivers/char/n_tty.c
--- a/drivers/char/n_tty.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by
+++ a/drivers/char/n_tty.c
@@ -1537,7 +1537,8 @@ static unsigned int normal_poll(struct t
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 -puN drivers/char/tty_io.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by drivers/char/tty_io.c
--- a/drivers/char/tty_io.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by
+++ a/drivers/char/tty_io.c
@@ -1719,6 +1719,23 @@ static ssize_t tty_read(struct file * fi
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
@@ -1730,13 +1747,12 @@ 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
@@ -1769,8 +1785,8 @@ 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;
@@ -1805,7 +1821,8 @@ 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;
}
@@ -3156,14 +3173,13 @@ static int tiocsetd(struct tty_struct *t
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 -puN drivers/char/tty_ioctl.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by drivers/char/tty_ioctl.c
--- a/drivers/char/tty_ioctl.c~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by
+++ a/drivers/char/tty_ioctl.c
@@ -667,7 +667,7 @@ static int send_prio_char(struct tty_str
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_str
tty->driver->write(tty, &ch, 1);
if (was_stopped)
stop_tty(tty);
- mutex_unlock(&tty->atomic_write_lock);
+ tty_write_unlock(tty);
return 0;
}
diff -puN include/linux/tty.h~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by include/linux/tty.h
--- a/include/linux/tty.h~prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by
+++ a/include/linux/tty.h
@@ -338,6 +338,12 @@ extern struct tty_struct *get_current_tt
extern struct mutex tty_mutex;
+extern void tty_write_unlock(struct tty_struct *tty);
+extern int tty_write_lock(struct tty_struct *tty, int ndelay);
+#define tty_is_writelocked(tty) (mutex_is_locked(&tty->atomic_write_lock))
+
+
+
/* n_tty.c */
extern struct tty_ldisc tty_ldisc_N_TTY;
_
Patches currently in -mm which might be from alan@xxxxxxxxxx are
libata-acpi-add-infrastructure-for-drivers-to-use.patch
pata_acpi-restore-driver.patch
pata_ali-more-work.patch
sl82c105-switch-to-ref-counting-api.patch
watchdog-documentation.patch
prevent-an-o_ndelay-writer-from-blocking-when-a-tty-write-is-blocked-by.patch
revoke-special-mmap-handling.patch
revoke-add-documentation.patch
revoke-wire-up-i386-system-calls.patch
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