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Subject[PATCH linux-next] tty: Fix lock order in tty_do_resize()
Date
Commits 6a1c0680cf3ba94356ecd58833e1540c93472a57 and
9356b535fcb71db494fc434acceb79f56d15bda2, respectively
'tty: Convert termios_mutex to termios_rwsem' and
'n_tty: Access termios values safely'
introduced a circular lock dependency with console_lock and
termios_rwsem.

The lockdep report [1] shows that n_tty_write() will attempt
to claim console_lock while holding the termios_rwsem, whereas
tty_do_resize() may already hold the console_lock while
claiming the termios_rwsem.

Since n_tty_write() and tty_do_resize() do not contend
over the same data -- the tty->winsize structure -- correct
the lock dependency by introducing a new lock which
specifically serializes access to tty->winsize only.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>

[1] Lockdep report

======================================================
[ INFO: possible circular locking dependency detected ]
3.10.0-0+tip-xeon+lockdep #0+tip Not tainted
-------------------------------------------------------
modprobe/277 is trying to acquire lock:
(&tty->termios_rwsem){++++..}, at: [<ffffffff81452656>] tty_do_resize+0x36/0xe0

but task is already holding lock:
((fb_notifier_list).rwsem){.+.+.+}, at: [<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #2 ((fb_notifier_list).rwsem){.+.+.+}:
[<ffffffff810b6d62>] lock_acquire+0x92/0x1f0
[<ffffffff8175b797>] down_read+0x47/0x5c
[<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0
[<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20
[<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20
[<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320
[<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper]
[<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau]
[<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau]
[<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm]
[<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau]
[<ffffffff813b13db>] local_pci_probe+0x4b/0x80
[<ffffffff813b1701>] pci_device_probe+0x111/0x120
[<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0
[<ffffffff81497bab>] __driver_attach+0xab/0xb0
[<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0
[<ffffffff814971fe>] driver_attach+0x1e/0x20
[<ffffffff81496cc1>] bus_add_driver+0x111/0x290
[<ffffffff814982b7>] driver_register+0x77/0x170
[<ffffffff813b0454>] __pci_register_driver+0x64/0x70
[<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm]
[<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau]
[<ffffffff810002ea>] do_one_initcall+0xea/0x1a0
[<ffffffff810c54cb>] load_module+0x123b/0x1bf0
[<ffffffff810c5f57>] SyS_init_module+0xd7/0x120
[<ffffffff817677c2>] system_call_fastpath+0x16/0x1b

-> #1 (console_lock){+.+.+.}:
[<ffffffff810b6d62>] lock_acquire+0x92/0x1f0
[<ffffffff810430a7>] console_lock+0x77/0x80
[<ffffffff8146b2a1>] con_flush_chars+0x31/0x50
[<ffffffff8145780c>] n_tty_write+0x1ec/0x4d0
[<ffffffff814541b9>] tty_write+0x159/0x2e0
[<ffffffff814543f5>] redirected_tty_write+0xb5/0xc0
[<ffffffff811ab9d5>] vfs_write+0xc5/0x1f0
[<ffffffff811abec5>] SyS_write+0x55/0xa0
[<ffffffff817677c2>] system_call_fastpath+0x16/0x1b

-> #0 (&tty->termios_rwsem){++++..}:
[<ffffffff810b65c3>] __lock_acquire+0x1c43/0x1d30
[<ffffffff810b6d62>] lock_acquire+0x92/0x1f0
[<ffffffff8175b724>] down_write+0x44/0x70
[<ffffffff81452656>] tty_do_resize+0x36/0xe0
[<ffffffff8146c841>] vc_do_resize+0x3e1/0x4c0
[<ffffffff8146c99f>] vc_resize+0x1f/0x30
[<ffffffff813e4535>] fbcon_init+0x385/0x5a0
[<ffffffff8146a4bc>] visual_init+0xbc/0x120
[<ffffffff8146cd13>] do_bind_con_driver+0x163/0x320
[<ffffffff8146cfa1>] do_take_over_console+0x61/0x70
[<ffffffff813e2b93>] do_fbcon_takeover+0x63/0xc0
[<ffffffff813e67a5>] fbcon_event_notify+0x715/0x820
[<ffffffff81762f9d>] notifier_call_chain+0x5d/0x110
[<ffffffff8107aadc>] __blocking_notifier_call_chain+0x6c/0xc0
[<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20
[<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20
[<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320
[<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper]
[<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau]
[<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau]
[<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm]
[<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau]
[<ffffffff813b13db>] local_pci_probe+0x4b/0x80
[<ffffffff813b1701>] pci_device_probe+0x111/0x120
[<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0
[<ffffffff81497bab>] __driver_attach+0xab/0xb0
[<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0
[<ffffffff814971fe>] driver_attach+0x1e/0x20
[<ffffffff81496cc1>] bus_add_driver+0x111/0x290
[<ffffffff814982b7>] driver_register+0x77/0x170
[<ffffffff813b0454>] __pci_register_driver+0x64/0x70
[<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm]
[<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau]
[<ffffffff810002ea>] do_one_initcall+0xea/0x1a0
[<ffffffff810c54cb>] load_module+0x123b/0x1bf0
[<ffffffff810c5f57>] SyS_init_module+0xd7/0x120
[<ffffffff817677c2>] system_call_fastpath+0x16/0x1b

other info that might help us debug this:

Chain exists of:
&tty->termios_rwsem --> console_lock --> (fb_notifier_list).rwsem

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock((fb_notifier_list).rwsem);
lock(console_lock);
lock((fb_notifier_list).rwsem);
lock(&tty->termios_rwsem);

*** DEADLOCK ***

7 locks held by modprobe/277:
#0: (&__lockdep_no_validate__){......}, at: [<ffffffff81497b5b>] __driver_attach+0x5b/0xb0
#1: (&__lockdep_no_validate__){......}, at: [<ffffffff81497b69>] __driver_attach+0x69/0xb0
#2: (drm_global_mutex){+.+.+.}, at: [<ffffffffa008a6dd>] drm_get_pci_dev+0xbd/0x2a0 [drm]
#3: (registration_lock){+.+.+.}, at: [<ffffffff813d93f5>] register_framebuffer+0x25/0x320
#4: (&fb_info->lock){+.+.+.}, at: [<ffffffff813d8116>] lock_fb_info+0x26/0x60
#5: (console_lock){+.+.+.}, at: [<ffffffff813d95a4>] register_framebuffer+0x1d4/0x320
#6: ((fb_notifier_list).rwsem){.+.+.+}, at: [<ffffffff8107aac6>] __blocking_notifier_call_chain+0x56/0xc0

stack backtrace:
CPU: 0 PID: 277 Comm: modprobe Not tainted 3.10.0-0+tip-xeon+lockdep #0+tip
Hardware name: Dell Inc. Precision WorkStation T5400 /0RW203, BIOS A11 04/30/2012
ffffffff8213e5e0 ffff8802aa2fb298 ffffffff81755f19 ffff8802aa2fb2e8
ffffffff8174f506 ffff8802aa2fa000 ffff8802aa2fb378 ffff8802aa2ea8e8
ffff8802aa2ea910 ffff8802aa2ea8e8 0000000000000006 0000000000000007
Call Trace:
[<ffffffff81755f19>] dump_stack+0x19/0x1b
[<ffffffff8174f506>] print_circular_bug+0x1fb/0x20c
[<ffffffff810b65c3>] __lock_acquire+0x1c43/0x1d30
[<ffffffff810b775e>] ? mark_held_locks+0xae/0x120
[<ffffffff810b78d5>] ? trace_hardirqs_on_caller+0x105/0x1d0
[<ffffffff810b6d62>] lock_acquire+0x92/0x1f0
[<ffffffff81452656>] ? tty_do_resize+0x36/0xe0
[<ffffffff8175b724>] down_write+0x44/0x70
[<ffffffff81452656>] ? tty_do_resize+0x36/0xe0
[<ffffffff81452656>] tty_do_resize+0x36/0xe0
[<ffffffff8146c841>] vc_do_resize+0x3e1/0x4c0
[<ffffffff8146c99f>] vc_resize+0x1f/0x30
[<ffffffff813e4535>] fbcon_init+0x385/0x5a0
[<ffffffff8146a4bc>] visual_init+0xbc/0x120
[<ffffffff8146cd13>] do_bind_con_driver+0x163/0x320
[<ffffffff8146cfa1>] do_take_over_console+0x61/0x70
[<ffffffff813e2b93>] do_fbcon_takeover+0x63/0xc0
[<ffffffff813e67a5>] fbcon_event_notify+0x715/0x820
[<ffffffff81762f9d>] notifier_call_chain+0x5d/0x110
[<ffffffff8107aadc>] __blocking_notifier_call_chain+0x6c/0xc0
[<ffffffff8107ab46>] blocking_notifier_call_chain+0x16/0x20
[<ffffffff813d7c0b>] fb_notifier_call_chain+0x1b/0x20
[<ffffffff813d95b2>] register_framebuffer+0x1e2/0x320
[<ffffffffa01043e1>] drm_fb_helper_initial_config+0x371/0x540 [drm_kms_helper]
[<ffffffff8173cbcb>] ? kmemleak_alloc+0x5b/0xc0
[<ffffffff81198874>] ? kmem_cache_alloc_trace+0x104/0x290
[<ffffffffa01035e1>] ? drm_fb_helper_single_add_all_connectors+0x81/0xf0 [drm_kms_helper]
[<ffffffffa01bcb05>] nouveau_fbcon_init+0x105/0x140 [nouveau]
[<ffffffffa01ad0af>] nouveau_drm_load+0x43f/0x610 [nouveau]
[<ffffffffa008a79e>] drm_get_pci_dev+0x17e/0x2a0 [drm]
[<ffffffffa01ad4da>] nouveau_drm_probe+0x25a/0x2a0 [nouveau]
[<ffffffff8175f162>] ? _raw_spin_unlock_irqrestore+0x42/0x80
[<ffffffff813b13db>] local_pci_probe+0x4b/0x80
[<ffffffff813b1701>] pci_device_probe+0x111/0x120
[<ffffffff814977eb>] driver_probe_device+0x8b/0x3a0
[<ffffffff81497bab>] __driver_attach+0xab/0xb0
[<ffffffff81497b00>] ? driver_probe_device+0x3a0/0x3a0
[<ffffffff814956ad>] bus_for_each_dev+0x5d/0xa0
[<ffffffff814971fe>] driver_attach+0x1e/0x20
[<ffffffff81496cc1>] bus_add_driver+0x111/0x290
[<ffffffffa022a000>] ? 0xffffffffa0229fff
[<ffffffff814982b7>] driver_register+0x77/0x170
[<ffffffffa022a000>] ? 0xffffffffa0229fff
[<ffffffff813b0454>] __pci_register_driver+0x64/0x70
[<ffffffffa008a9da>] drm_pci_init+0x11a/0x130 [drm]
[<ffffffffa022a000>] ? 0xffffffffa0229fff
[<ffffffffa022a000>] ? 0xffffffffa0229fff
[<ffffffffa022a04d>] nouveau_drm_init+0x4d/0x1000 [nouveau]
[<ffffffff810002ea>] do_one_initcall+0xea/0x1a0
[<ffffffff810c54cb>] load_module+0x123b/0x1bf0
[<ffffffff81399a50>] ? ddebug_proc_open+0xb0/0xb0
[<ffffffff813855ae>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff810c5f57>] SyS_init_module+0xd7/0x120
[<ffffffff817677c2>] system_call_fastpath+0x16/0x1b
---
drivers/tty/pty.c | 4 ++--
drivers/tty/tty_io.c | 11 ++++++-----
include/linux/tty.h | 3 ++-
3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
index b940127..25c9bc7 100644
--- a/drivers/tty/pty.c
+++ b/drivers/tty/pty.c
@@ -281,7 +281,7 @@ static int pty_resize(struct tty_struct *tty, struct winsize *ws)
struct tty_struct *pty = tty->link;

/* For a PTY we need to lock the tty side */
- down_write(&tty->termios_rwsem);
+ mutex_lock(&tty->winsize_mutex);
if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
goto done;

@@ -308,7 +308,7 @@ static int pty_resize(struct tty_struct *tty, struct winsize *ws)
tty->winsize = *ws;
pty->winsize = *ws; /* Never used so will go away soon */
done:
- up_write(&tty->termios_rwsem);
+ mutex_unlock(&tty->winsize_mutex);
return 0;
}

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 2174698..26bb78c 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2229,7 +2229,7 @@ static int tiocsti(struct tty_struct *tty, char __user *p)
*
* Copies the kernel idea of the window size into the user buffer.
*
- * Locking: tty->termios_rwsem is taken to ensure the winsize data
+ * Locking: tty->winsize_mutex is taken to ensure the winsize data
* is consistent.
*/

@@ -2237,9 +2237,9 @@ static int tiocgwinsz(struct tty_struct *tty, struct winsize __user *arg)
{
int err;

- down_read(&tty->termios_rwsem);
+ mutex_lock(&tty->winsize_mutex);
err = copy_to_user(arg, &tty->winsize, sizeof(*arg));
- up_read(&tty->termios_rwsem);
+ mutex_unlock(&tty->winsize_mutex);

return err ? -EFAULT: 0;
}
@@ -2260,7 +2260,7 @@ int tty_do_resize(struct tty_struct *tty, struct winsize *ws)
unsigned long flags;

/* Lock the tty */
- down_write(&tty->termios_rwsem);
+ mutex_lock(&tty->winsize_mutex);
if (!memcmp(ws, &tty->winsize, sizeof(*ws)))
goto done;
/* Get the PID values and reference them so we can
@@ -2275,7 +2275,7 @@ int tty_do_resize(struct tty_struct *tty, struct winsize *ws)

tty->winsize = *ws;
done:
- up_write(&tty->termios_rwsem);
+ mutex_unlock(&tty->winsize_mutex);
return 0;
}
EXPORT_SYMBOL(tty_do_resize);
@@ -3016,6 +3016,7 @@ void initialize_tty_struct(struct tty_struct *tty,
mutex_init(&tty->legacy_mutex);
mutex_init(&tty->throttle_mutex);
init_rwsem(&tty->termios_rwsem);
+ mutex_init(&tty->winsize_mutex);
init_ldsem(&tty->ldisc_sem);
init_waitqueue_head(&tty->write_wait);
init_waitqueue_head(&tty->read_wait);
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 8f671b2..5c99f9d 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -245,6 +245,7 @@ struct tty_struct {
struct mutex legacy_mutex;
struct mutex throttle_mutex;
struct rw_semaphore termios_rwsem;
+ struct mutex winsize_mutex;
spinlock_t ctrl_lock;
/* Termios values are protected by the termios rwsem */
struct ktermios termios, termios_locked;
@@ -254,7 +255,7 @@ struct tty_struct {
struct pid *session;
unsigned long flags;
int count;
- struct winsize winsize; /* termios rwsem */
+ struct winsize winsize; /* winsize_mutex */
unsigned char stopped:1, hw_stopped:1, flow_stopped:1, packet:1;
unsigned char ctrl_status; /* ctrl_lock */
unsigned int receive_room; /* Bytes free for queue */
--
1.8.1.2


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