[PATCH 6/6] tty: Make tty_files_lock per-tty

Peter Hurley
2015-11-28T02:39:05Z

Access to tty->tty_files list is always per-tty, never for all ttys
simultaneously. Replace global tty_files_lock spinlock with per-tty
->files_lock. Initialize when the ->tty_files list is inited, in
alloc_tty_struct().

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
drivers/tty/tty_io.c | 25 ++++++++++++-------------
include/linux/tty.h | 2 +-
security/selinux/hooks.c | 4 ++--
3 files changed, 15 insertions(+), 16 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a8a1f62..5c8f519 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -138,9 +138,6 @@ LIST_HEAD(tty_drivers); /* linked list of tty drivers */
/* Mutex to protect creating and releasing a tty */
DEFINE_MUTEX(tty_mutex);

-/* Spinlock to protect the tty->tty_files list */
-DEFINE_SPINLOCK(tty_files_lock);
-
static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
static ssize_t tty_write(struct file *, const char __user *, size_t, loff_t *);
ssize_t redirected_tty_write(struct file *, const char __user *,
@@ -202,9 +199,9 @@ void tty_add_file(struct tty_struct *tty, struct file *file)
priv->tty = tty;
priv->file = file;

- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
list_add(&priv->list, &tty->tty_files);
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);
}

/**
@@ -225,10 +222,11 @@ void tty_free_file(struct file *file)
static void tty_del_file(struct file *file)
{
struct tty_file_private *priv = file->private_data;
+ struct tty_struct *tty = priv->tty;

- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
list_del(&priv->list);
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);
tty_free_file(file);
}

@@ -286,11 +284,11 @@ static int check_tty_count(struct tty_struct *tty, const char *routine)
struct list_head *p;
int count = 0;

- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
list_for_each(p, &tty->tty_files) {
count++;
}
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);
if (tty->driver->type == TTY_DRIVER_TYPE_PTY &&
tty->driver->subtype == PTY_TYPE_SLAVE &&
tty->link && tty->link->count)
@@ -713,7 +711,7 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
workqueue with the lock held */
check_tty_count(tty, "tty_hangup");

- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
/* This breaks for file handles being sent over AF_UNIX sockets ? */
list_for_each_entry(priv, &tty->tty_files, list) {
filp = priv->file;
@@ -725,7 +723,7 @@ static void __tty_hangup(struct tty_struct *tty, int exit_session)
__tty_fasync(-1, filp, 0); /* can't block */
filp->f_op = &hung_up_tty_fops;
}
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);

refs = tty_signal_session_leader(tty, exit_session);
/* Account for the p->signal references we killed */
@@ -1641,9 +1639,9 @@ static void release_one_tty(struct work_struct *work)
tty_driver_kref_put(driver);
module_put(owner);

- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
list_del_init(&tty->tty_files);
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);

put_pid(tty->pgrp);
put_pid(tty->session);
@@ -3166,6 +3164,7 @@ struct tty_struct *alloc_tty_struct(struct tty_driver *driver, int idx)
mutex_init(&tty->atomic_write_lock);
spin_lock_init(&tty->ctrl_lock);
spin_lock_init(&tty->flow_lock);
+ spin_lock_init(&tty->files_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 168f198..a2d167e 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -302,6 +302,7 @@ struct tty_struct {
struct work_struct hangup_work;
void *disc_data;
void *driver_data;
+ spinlock_t files_lock; /* protects tty_files list */
struct list_head tty_files;

#define N_TTY_BUF_SIZE 4096
@@ -509,7 +510,6 @@ extern int tty_standard_install(struct tty_driver *driver,
struct tty_struct *tty);

extern struct mutex tty_mutex;
-extern spinlock_t tty_files_lock;

#define tty_is_writelocked(tty) (mutex_is_locked(&tty->atomic_write_lock))

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index d0cfaa9..ae6dbc75 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2352,7 +2352,7 @@ static inline void flush_unauthorized_files(const struct cred *cred,

tty = get_current_tty();
if (tty) {
- spin_lock(&tty_files_lock);
+ spin_lock(&tty->files_lock);
if (!list_empty(&tty->tty_files)) {
struct tty_file_private *file_priv;

@@ -2367,7 +2367,7 @@ static inline void flush_unauthorized_files(const struct cred *cred,
if (file_path_has_perm(cred, file, FILE__READ | FILE__WRITE))
drop_tty = 1;
}
- spin_unlock(&tty_files_lock);
+ spin_unlock(&tty->files_lock);
tty_kref_put(tty);
}
/* Reset controlling tty. */
--
2.6.3