The patch titled
do_tty_write() can block even with O_NONBLOCK?
has been added to the -mm tree. Its filename is
do_tty_write-can-block-even-with-o_nonblock.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: do_tty_write() can block even with O_NONBLOCK?
From: Dave Johnson <djohnson+linux-kernel@xxxxxxxxxxxxxxxxxxxxxx>
I have two processes with the same tty open, one opens blocking and one
opens nonblocking.
If the blocking process blocks doing a write (due to flow control, just
going to fast, etc...) the nonblocking process will also block when it
writes until the blocking process unblocks.
This seems to occur because do_tty_write() isn't checking for O_NONBLOCK
when taking the tty's write mutex.
Signed-off-by: Dave Johnson <djohnson+linux-kernel@xxxxxxxxxxxxxxxxxxxxxx>
Acked-by: Alan Cox <alan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/char/tty_io.c | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff -puN drivers/char/tty_io.c~do_tty_write-can-block-even-with-o_nonblock drivers/char/tty_io.c
--- a/drivers/char/tty_io.c~do_tty_write-can-block-even-with-o_nonblock
+++ a/drivers/char/tty_io.c
@@ -1699,9 +1699,13 @@ static inline ssize_t do_tty_write(
ssize_t ret = 0, written = 0;
unsigned int chunk;
- /* FIXME: O_NDELAY ... */
- if (mutex_lock_interruptible(&tty->atomic_write_lock)) {
- return -ERESTARTSYS;
+ if (file->f_flags & O_NONBLOCK) {
+ if (!mutex_trylock(&tty->atomic_write_lock))
+ return -EAGAIN;
+ }
+ else {
+ if (mutex_lock_interruptible(&tty->atomic_write_lock))
+ return -ERESTARTSYS;
}
/*
_
Patches currently in -mm which might be from djohnson+linux-kernel@xxxxxxxxxxxxxxxxxxxxxx are
do_tty_write-can-block-even-with-o_nonblock.patch
do_tty_write-can-block-even-with-o_nonblock-tidy.patch
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