Commit 82a1601e authored by Peter Hurley's avatar Peter Hurley Committed by Luis Henriques

tty: Fix high cpu load if tty is unreleaseable

commit 37b16457 upstream.

Kernel oops can cause the tty to be unreleaseable (for example, if
n_tty_read() crashes while on the read_wait queue). This will cause
tty_release() to endlessly loop without sleeping.

Use a killable sleep timeout which grows by 2n+1 jiffies over the interval
[0, 120 secs.) and then jumps to forever (but still killable).

NB: killable just allows for the task to be rewoken manually, not
to be terminated.
Signed-off-by: default avatarPeter Hurley <peter@hurleysoftware.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 2f590344
...@@ -1701,6 +1701,7 @@ int tty_release(struct inode *inode, struct file *filp) ...@@ -1701,6 +1701,7 @@ int tty_release(struct inode *inode, struct file *filp)
int pty_master, tty_closing, o_tty_closing, do_sleep; int pty_master, tty_closing, o_tty_closing, do_sleep;
int idx; int idx;
char buf[64]; char buf[64];
long timeout = 0;
if (tty_paranoia_check(tty, inode, __func__)) if (tty_paranoia_check(tty, inode, __func__))
return 0; return 0;
...@@ -1785,7 +1786,11 @@ int tty_release(struct inode *inode, struct file *filp) ...@@ -1785,7 +1786,11 @@ int tty_release(struct inode *inode, struct file *filp)
__func__, tty_name(tty, buf)); __func__, tty_name(tty, buf));
tty_unlock_pair(tty, o_tty); tty_unlock_pair(tty, o_tty);
mutex_unlock(&tty_mutex); mutex_unlock(&tty_mutex);
schedule(); schedule_timeout_killable(timeout);
if (timeout < 120 * HZ)
timeout = 2 * timeout + 1;
else
timeout = MAX_SCHEDULE_TIMEOUT;
} }
/* /*
......
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