Hi Peter,
This bug was founded in RHEL 6, kernel version 2.6.32.
But I also checked the file tty_io.c in latest kernel, not all the code
protected by tty_lock(tty).
For example, in function tty_del_file,
if (--tty->count < 0) {
}
and
tty_del_file(filp);
are not surrounded by tty_lock(tty).
So I think the new lock is necessary.
Thanks
Zhenhua
On 07/14/2014 08:25 PM, Peter Hurley wrote:
Hi Zhen-Hua,
On 07/14/2014 01:54 AM, Li, Zhen-Hua wrote:
When there are to many open/close on a tty device in the same time,
there may be a warning like:
Warning: dev (ttyS0) tty->count(4) != #fd's(3) in tty_release_dev
That's because tty->count and files in tty->tty_files are not
synchronized
in time.
So I add a lock to avoid this.
Every place you added the count_lock spinlock is already protected
by tty_lock(tty), so the count is out of sync for some other reason.
What kernel version are you having this problem on and what are the
circumstances?
Regards,
Peter Hurley
Signed-off-by: Li, Zhen-Hua <zhen-h...@hp.com>
---
drivers/tty/tty_io.c | 13 +++++++++----
include/linux/tty.h | 1 +
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 3411071..9283fc2 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -297,6 +297,7 @@ static int check_tty_count(struct tty_struct
*tty, const char *routine)
struct list_head *p;
int count = 0;
+ spin_lock(&tty->count_lock);
spin_lock(&tty_files_lock);
list_for_each(p, &tty->tty_files) {
count++;
@@ -310,8 +311,10 @@ static int check_tty_count(struct tty_struct
*tty, const char *routine)
printk(KERN_WARNING "Warning: dev (%s) tty->count(%d) "
"!= #fd's(%d) in %s\n",
tty->name, tty->count, count, routine);
+ spin_unlock(&tty->count_lock);
return count;
}
+ spin_unlock(&tty->count_lock);
#endif
return 0;
}
@@ -1337,7 +1340,6 @@ int tty_standard_install(struct tty_driver
*driver, struct tty_struct *tty)
return ret;
tty_driver_kref_get(driver);
- tty->count++;
driver->ttys[tty->index] = tty;
return 0;
}
@@ -1408,7 +1410,6 @@ static int tty_reopen(struct tty_struct *tty)
tty->link->count++;
}
- tty->count++;
WARN_ON(!tty->ldisc);
@@ -1796,6 +1797,7 @@ int tty_release(struct inode *inode, struct
file *filp)
* We must *not* drop the tty_mutex until we ensure that a further
* entry into tty_open can not pick up this tty.
*/
+ spin_lock(&tty->count_lock);
if (pty_master) {
if (--o_tty->count < 0) {
printk(KERN_WARNING "%s: bad pty slave count (%d) for
%s\n",
@@ -1819,7 +1821,7 @@ int tty_release(struct inode *inode, struct
file *filp)
* something that needs to be handled for hangups.
*/
tty_del_file(filp);
-
+ spin_unlock(&tty->count_lock);
/*
* Perform some housekeeping before deciding whether to return.
*
@@ -2046,8 +2048,10 @@ retry_open:
retval = PTR_ERR(tty);
goto err_file;
}
-
+ spin_lock(&tty->count_lock);
+ tty->count++;
tty_add_file(tty, filp);
+ spin_unlock(&tty->count_lock);
check_tty_count(tty, __func__);
if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
@@ -3031,6 +3035,7 @@ void initialize_tty_struct(struct tty_struct *tty,
INIT_WORK(&tty->hangup_work, do_tty_hangup);
mutex_init(&tty->atomic_write_lock);
spin_lock_init(&tty->ctrl_lock);
+ spin_lock_init(&tty->count_lock);
INIT_LIST_HEAD(&tty->tty_files);
INIT_WORK(&tty->SAK_work, do_SAK_work);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 1c3316a..2959300 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -284,6 +284,7 @@ struct tty_struct {
/* If the tty has a pending do_SAK, queue it here - akpm */
struct work_struct SAK_work;
struct tty_port *port;
+ spinlock_t count_lock;
};
/* Each of a tty's open files has private_data pointing to
tty_file_private */
--
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