* [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
[not found] <20130731114726.GA11570@cpv436-motbuntu.spb.ea.mot-mobility.com>
@ 2013-08-11 12:04 ` Peter Hurley
2013-08-12 9:28 ` Artem Savkov
0 siblings, 1 reply; 7+ messages in thread
From: Peter Hurley @ 2013-08-11 12:04 UTC (permalink / raw)
To: Greg Kroah-Hartman
Cc: linux-next, linux-kernel, Jiri Slaby, Artem Savkov,
Sergey Senozhatsky, Belisko Marek, Peter Hurley
Lockdep reports a circular lock dependency between
atomic_read_lock and termios_rwsem [1]. However, a lock
order deadlock is not possible since CPU1 only holds a
read lock which cannot prevent CPU0 from also acquiring
a read lock on the same r/w semaphore.
Unfortunately, lockdep cannot currently distinguish whether
the locks are read or write for any particular lock graph,
merely that the locks _were_ previously read and/or write.
Until lockdep is fixed, re-order atomic_read_lock so
termios_rwsem can be dropped and reacquired without
triggering lockdep.
Reported-by: Artem Savkov <artem.savkov@gmail.com>
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
[1] Initial lockdep report from Artem Savkov <artem.savkov@gmail.com>
======================================================
[ INFO: possible circular locking dependency detected ]
3.11.0-rc3-next-20130730+ #140 Tainted: G W
-------------------------------------------------------
bash/1198 is trying to acquire lock:
(&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
but task is already holding lock:
(&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&ldata->atomic_read_lock){+.+...}:
[<ffffffff811111cc>] validate_chain+0x73c/0x850
[<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
[<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
[<ffffffff816a3bb6>] tty_read+0x86/0xf0
[<ffffffff811f21d3>] vfs_read+0xc3/0x130
[<ffffffff811f2702>] SyS_read+0x62/0xa0
[<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
-> #0 (&tty->termios_rwsem){++++..}:
[<ffffffff8111064f>] check_prev_add+0x14f/0x590
[<ffffffff811111cc>] validate_chain+0x73c/0x850
[<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[<ffffffff81d372c1>] down_read+0x51/0xa0
[<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
[<ffffffff816a3bb6>] tty_read+0x86/0xf0
[<ffffffff811f21d3>] vfs_read+0xc3/0x130
[<ffffffff811f2702>] SyS_read+0x62/0xa0
[<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&ldata->atomic_read_lock);
lock(&tty->termios_rwsem);
lock(&ldata->atomic_read_lock);
lock(&tty->termios_rwsem);
*** DEADLOCK ***
2 locks held by bash/1198:
#0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
#1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
stack backtrace:
CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
Call Trace:
[<ffffffff81d34074>] dump_stack+0x59/0x7d
[<ffffffff8110ed75>] print_circular_bug+0x105/0x120
[<ffffffff8111064f>] check_prev_add+0x14f/0x590
[<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
[<ffffffff811111cc>] validate_chain+0x73c/0x850
[<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
[<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
[<ffffffff81d372c1>] down_read+0x51/0xa0
[<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
[<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
[<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
[<ffffffff816a3bb6>] tty_read+0x86/0xf0
[<ffffffff811f21d3>] vfs_read+0xc3/0x130
[<ffffffff811f2702>] SyS_read+0x62/0xa0
[<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
---
drivers/tty/n_tty.c | 25 +++++++++++--------------
1 file changed, 11 insertions(+), 14 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index dd8ae0c..c9a9ddd 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2122,6 +2122,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
if (c < 0)
return c;
+ /*
+ * Internal serialization of reads.
+ */
+ if (file->f_flags & O_NONBLOCK) {
+ if (!mutex_trylock(&ldata->atomic_read_lock))
+ return -EAGAIN;
+ } else {
+ if (mutex_lock_interruptible(&ldata->atomic_read_lock))
+ return -ERESTARTSYS;
+ }
+
down_read(&tty->termios_rwsem);
minimum = time = 0;
@@ -2141,20 +2152,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
}
}
- /*
- * Internal serialization of reads.
- */
- if (file->f_flags & O_NONBLOCK) {
- if (!mutex_trylock(&ldata->atomic_read_lock)) {
- up_read(&tty->termios_rwsem);
- return -EAGAIN;
- }
- } else {
- if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
- up_read(&tty->termios_rwsem);
- return -ERESTARTSYS;
- }
- }
packet = tty->packet;
add_wait_queue(&tty->read_wait, &wait);
--
1.8.1.2
^ permalink raw reply related [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-11 12:04 ` [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive Peter Hurley
@ 2013-08-12 9:28 ` Artem Savkov
2013-08-12 10:50 ` Sergey Senozhatsky
0 siblings, 1 reply; 7+ messages in thread
From: Artem Savkov @ 2013-08-12 9:28 UTC (permalink / raw)
To: Peter Hurley
Cc: Greg Kroah-Hartman, linux-next, linux-kernel, Jiri Slaby,
Sergey Senozhatsky, Belisko Marek
Hi Peter,
On Sun, Aug 11, 2013 at 08:04:23AM -0400, Peter Hurley wrote:
> Lockdep reports a circular lock dependency between
> atomic_read_lock and termios_rwsem [1]. However, a lock
> order deadlock is not possible since CPU1 only holds a
> read lock which cannot prevent CPU0 from also acquiring
> a read lock on the same r/w semaphore.
>
> Unfortunately, lockdep cannot currently distinguish whether
> the locks are read or write for any particular lock graph,
> merely that the locks _were_ previously read and/or write.
>
> Until lockdep is fixed, re-order atomic_read_lock so
> termios_rwsem can be dropped and reacquired without
> triggering lockdep.
Works fine, thanks.
Reported-and-tested-by: Artem Savkov <artem.savkov@gmail.com>
> Reported-by: Artem Savkov <artem.savkov@gmail.com>
> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
>
> [1] Initial lockdep report from Artem Savkov <artem.savkov@gmail.com>
>
> ======================================================
> [ INFO: possible circular locking dependency detected ]
> 3.11.0-rc3-next-20130730+ #140 Tainted: G W
> -------------------------------------------------------
> bash/1198 is trying to acquire lock:
> (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>
> but task is already holding lock:
> (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #1 (&ldata->atomic_read_lock){+.+...}:
> [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
> [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>
> -> #0 (&tty->termios_rwsem){++++..}:
> [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [<ffffffff81d372c1>] down_read+0x51/0xa0
> [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>
> other info that might help us debug this:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&ldata->atomic_read_lock);
> lock(&tty->termios_rwsem);
> lock(&ldata->atomic_read_lock);
> lock(&tty->termios_rwsem);
>
> *** DEADLOCK ***
>
> 2 locks held by bash/1198:
> #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
> #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>
> stack backtrace:
> CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
> 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
> ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
> Call Trace:
> [<ffffffff81d34074>] dump_stack+0x59/0x7d
> [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
> [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
> [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> [<ffffffff81d372c1>] down_read+0x51/0xa0
> [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> ---
> drivers/tty/n_tty.c | 25 +++++++++++--------------
> 1 file changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index dd8ae0c..c9a9ddd 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -2122,6 +2122,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> if (c < 0)
> return c;
>
> + /*
> + * Internal serialization of reads.
> + */
> + if (file->f_flags & O_NONBLOCK) {
> + if (!mutex_trylock(&ldata->atomic_read_lock))
> + return -EAGAIN;
> + } else {
> + if (mutex_lock_interruptible(&ldata->atomic_read_lock))
> + return -ERESTARTSYS;
> + }
> +
> down_read(&tty->termios_rwsem);
>
> minimum = time = 0;
> @@ -2141,20 +2152,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> }
> }
>
> - /*
> - * Internal serialization of reads.
> - */
> - if (file->f_flags & O_NONBLOCK) {
> - if (!mutex_trylock(&ldata->atomic_read_lock)) {
> - up_read(&tty->termios_rwsem);
> - return -EAGAIN;
> - }
> - } else {
> - if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
> - up_read(&tty->termios_rwsem);
> - return -ERESTARTSYS;
> - }
> - }
> packet = tty->packet;
>
> add_wait_queue(&tty->read_wait, &wait);
> --
> 1.8.1.2
>
--
Regards,
Artem
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-12 9:28 ` Artem Savkov
@ 2013-08-12 10:50 ` Sergey Senozhatsky
2013-08-12 12:55 ` Peter Hurley
0 siblings, 1 reply; 7+ messages in thread
From: Sergey Senozhatsky @ 2013-08-12 10:50 UTC (permalink / raw)
To: Peter Hurley, Greg Kroah-Hartman, linux-next, linux-kernel,
Jiri Slaby, Sergey Senozhatsky, Belisko Marek
On (08/12/13 13:28), Artem Savkov wrote:
> Hi Peter,
>
> On Sun, Aug 11, 2013 at 08:04:23AM -0400, Peter Hurley wrote:
> > Lockdep reports a circular lock dependency between
> > atomic_read_lock and termios_rwsem [1]. However, a lock
> > order deadlock is not possible since CPU1 only holds a
> > read lock which cannot prevent CPU0 from also acquiring
> > a read lock on the same r/w semaphore.
> >
> > Unfortunately, lockdep cannot currently distinguish whether
> > the locks are read or write for any particular lock graph,
> > merely that the locks _were_ previously read and/or write.
> >
> > Until lockdep is fixed, re-order atomic_read_lock so
> > termios_rwsem can be dropped and reacquired without
> > triggering lockdep.
>
> Works fine, thanks.
>
> Reported-and-tested-by: Artem Savkov <artem.savkov@gmail.com>
>
> > Reported-by: Artem Savkov <artem.savkov@gmail.com>
> > Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> > Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
> >
> > [1] Initial lockdep report from Artem Savkov <artem.savkov@gmail.com>
> >
> > ======================================================
> > [ INFO: possible circular locking dependency detected ]
> > 3.11.0-rc3-next-20130730+ #140 Tainted: G W
> > -------------------------------------------------------
> > bash/1198 is trying to acquire lock:
> > (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> >
> > but task is already holding lock:
> > (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> >
> > which lock already depends on the new lock.
> >
> > the existing dependency chain (in reverse order) is:
> >
> > -> #1 (&ldata->atomic_read_lock){+.+...}:
> > [<ffffffff811111cc>] validate_chain+0x73c/0x850
> > [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> > [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> > [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
> > [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> > [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> > [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> > [<ffffffff811f2702>] SyS_read+0x62/0xa0
> > [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> >
> > -> #0 (&tty->termios_rwsem){++++..}:
> > [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> > [<ffffffff811111cc>] validate_chain+0x73c/0x850
> > [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> > [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> > [<ffffffff81d372c1>] down_read+0x51/0xa0
> > [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> > [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> > [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> > [<ffffffff811f2702>] SyS_read+0x62/0xa0
> > [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> >
> > other info that might help us debug this:
> >
> > Possible unsafe locking scenario:
> >
> > CPU0 CPU1
> > ---- ----
> > lock(&ldata->atomic_read_lock);
> > lock(&tty->termios_rwsem);
> > lock(&ldata->atomic_read_lock);
> > lock(&tty->termios_rwsem);
> >
> > *** DEADLOCK ***
> >
> > 2 locks held by bash/1198:
> > #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
> > #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> >
> > stack backtrace:
> > CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
> > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> > 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
> > 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
> > ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
> > Call Trace:
> > [<ffffffff81d34074>] dump_stack+0x59/0x7d
> > [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
> > [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> > [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
> > [<ffffffff811111cc>] validate_chain+0x73c/0x850
> > [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
> > [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> > [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> > [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> > [<ffffffff81d372c1>] down_read+0x51/0xa0
> > [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> > [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> > [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
> > [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> > [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> > [<ffffffff811f2702>] SyS_read+0x62/0xa0
> > [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> > [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> > ---
> > drivers/tty/n_tty.c | 25 +++++++++++--------------
> > 1 file changed, 11 insertions(+), 14 deletions(-)
> >
I hate to do this, but isn't it actually my patch posted here
https://lkml.org/lkml/2013/8/1/510
which was tagged as `wrong'?
-ss
> > diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> > index dd8ae0c..c9a9ddd 100644
> > --- a/drivers/tty/n_tty.c
> > +++ b/drivers/tty/n_tty.c
> > @@ -2122,6 +2122,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> > if (c < 0)
> > return c;
> >
> > + /*
> > + * Internal serialization of reads.
> > + */
> > + if (file->f_flags & O_NONBLOCK) {
> > + if (!mutex_trylock(&ldata->atomic_read_lock))
> > + return -EAGAIN;
> > + } else {
> > + if (mutex_lock_interruptible(&ldata->atomic_read_lock))
> > + return -ERESTARTSYS;
> > + }
> > +
> > down_read(&tty->termios_rwsem);
> >
> > minimum = time = 0;
> > @@ -2141,20 +2152,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> > }
> > }
> >
> > - /*
> > - * Internal serialization of reads.
> > - */
> > - if (file->f_flags & O_NONBLOCK) {
> > - if (!mutex_trylock(&ldata->atomic_read_lock)) {
> > - up_read(&tty->termios_rwsem);
> > - return -EAGAIN;
> > - }
> > - } else {
> > - if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
> > - up_read(&tty->termios_rwsem);
> > - return -ERESTARTSYS;
> > - }
> > - }
> > packet = tty->packet;
> >
> > add_wait_queue(&tty->read_wait, &wait);
> > --
> > 1.8.1.2
> >
>
> --
> Regards,
> Artem
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-12 10:50 ` Sergey Senozhatsky
@ 2013-08-12 12:55 ` Peter Hurley
2013-08-12 13:19 ` Sergey Senozhatsky
0 siblings, 1 reply; 7+ messages in thread
From: Peter Hurley @ 2013-08-12 12:55 UTC (permalink / raw)
To: Sergey Senozhatsky
Cc: Greg Kroah-Hartman, linux-next, linux-kernel, Jiri Slaby, Belisko Marek
On 08/12/2013 06:50 AM, Sergey Senozhatsky wrote:
> On (08/12/13 13:28), Artem Savkov wrote:
>> Hi Peter,
>>
>> On Sun, Aug 11, 2013 at 08:04:23AM -0400, Peter Hurley wrote:
>>> Lockdep reports a circular lock dependency between
>>> atomic_read_lock and termios_rwsem [1]. However, a lock
>>> order deadlock is not possible since CPU1 only holds a
>>> read lock which cannot prevent CPU0 from also acquiring
>>> a read lock on the same r/w semaphore.
>>>
>>> Unfortunately, lockdep cannot currently distinguish whether
>>> the locks are read or write for any particular lock graph,
>>> merely that the locks _were_ previously read and/or write.
>>>
>>> Until lockdep is fixed, re-order atomic_read_lock so
>>> termios_rwsem can be dropped and reacquired without
>>> triggering lockdep.
>>
>> Works fine, thanks.
>>
>> Reported-and-tested-by: Artem Savkov <artem.savkov@gmail.com>
>>
>>> Reported-by: Artem Savkov <artem.savkov@gmail.com>
>>> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
>>> Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
>>>
>>> [1] Initial lockdep report from Artem Savkov <artem.savkov@gmail.com>
>>>
>>> ======================================================
>>> [ INFO: possible circular locking dependency detected ]
>>> 3.11.0-rc3-next-20130730+ #140 Tainted: G W
>>> -------------------------------------------------------
>>> bash/1198 is trying to acquire lock:
>>> (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>>>
>>> but task is already holding lock:
>>> (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>>>
>>> which lock already depends on the new lock.
>>>
>>> the existing dependency chain (in reverse order) is:
>>>
>>> -> #1 (&ldata->atomic_read_lock){+.+...}:
>>> [<ffffffff811111cc>] validate_chain+0x73c/0x850
>>> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
>>> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
>>> [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
>>> [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>>> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
>>> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
>>> [<ffffffff811f2702>] SyS_read+0x62/0xa0
>>> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>>>
>>> -> #0 (&tty->termios_rwsem){++++..}:
>>> [<ffffffff8111064f>] check_prev_add+0x14f/0x590
>>> [<ffffffff811111cc>] validate_chain+0x73c/0x850
>>> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
>>> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
>>> [<ffffffff81d372c1>] down_read+0x51/0xa0
>>> [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>>> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
>>> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
>>> [<ffffffff811f2702>] SyS_read+0x62/0xa0
>>> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>>>
>>> other info that might help us debug this:
>>>
>>> Possible unsafe locking scenario:
>>>
>>> CPU0 CPU1
>>> ---- ----
>>> lock(&ldata->atomic_read_lock);
>>> lock(&tty->termios_rwsem);
>>> lock(&ldata->atomic_read_lock);
>>> lock(&tty->termios_rwsem);
>>>
>>> *** DEADLOCK ***
>>>
>>> 2 locks held by bash/1198:
>>> #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
>>> #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>>>
>>> stack backtrace:
>>> CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
>>> Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
>>> 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
>>> 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
>>> ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
>>> Call Trace:
>>> [<ffffffff81d34074>] dump_stack+0x59/0x7d
>>> [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
>>> [<ffffffff8111064f>] check_prev_add+0x14f/0x590
>>> [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
>>> [<ffffffff811111cc>] validate_chain+0x73c/0x850
>>> [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
>>> [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
>>> [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
>>> [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
>>> [<ffffffff81d372c1>] down_read+0x51/0xa0
>>> [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
>>> [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>>> [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
>>> [<ffffffff816a3bb6>] tty_read+0x86/0xf0
>>> [<ffffffff811f21d3>] vfs_read+0xc3/0x130
>>> [<ffffffff811f2702>] SyS_read+0x62/0xa0
>>> [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>>> [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>>> ---
>>> drivers/tty/n_tty.c | 25 +++++++++++--------------
>>> 1 file changed, 11 insertions(+), 14 deletions(-)
>>>
>
> I hate to do this, but isn't it actually my patch posted here
> https://lkml.org/lkml/2013/8/1/510
>
> which was tagged as `wrong'?
Sergey,
My apologies; I was mistaken regarding this problem being a lockdep
regression (although it's still a false positive from lockdep). Once
I had worked around some issues with the nouveau driver, I was able to
reproduce the lockdep report on 3.10.
I included Artem's lockdep report in the changelog because I received
that first, on 30 July.
My patch below is not the same as your patch of 1 Aug. This patch
preserves the protected access of termios.c_cc[VMIN] and termios.c_cc[VTIME]
(via the MIN_CHAR() and TIME_CHAR() macros).
If you'd prefer, I could add to changelog:
Patch based on original posted here https://lkml.org/lkml/2013/8/1/510
by Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Regards,
Peter Hurley
>>> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
>>> index dd8ae0c..c9a9ddd 100644
>>> --- a/drivers/tty/n_tty.c
>>> +++ b/drivers/tty/n_tty.c
>>> @@ -2122,6 +2122,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
>>> if (c < 0)
>>> return c;
>>>
>>> + /*
>>> + * Internal serialization of reads.
>>> + */
>>> + if (file->f_flags & O_NONBLOCK) {
>>> + if (!mutex_trylock(&ldata->atomic_read_lock))
>>> + return -EAGAIN;
>>> + } else {
>>> + if (mutex_lock_interruptible(&ldata->atomic_read_lock))
>>> + return -ERESTARTSYS;
>>> + }
>>> +
>>> down_read(&tty->termios_rwsem);
>>>
>>> minimum = time = 0;
>>> @@ -2141,20 +2152,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
>>> }
>>> }
>>>
>>> - /*
>>> - * Internal serialization of reads.
>>> - */
>>> - if (file->f_flags & O_NONBLOCK) {
>>> - if (!mutex_trylock(&ldata->atomic_read_lock)) {
>>> - up_read(&tty->termios_rwsem);
>>> - return -EAGAIN;
>>> - }
>>> - } else {
>>> - if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
>>> - up_read(&tty->termios_rwsem);
>>> - return -ERESTARTSYS;
>>> - }
>>> - }
>>> packet = tty->packet;
>>>
>>> add_wait_queue(&tty->read_wait, &wait);
>>> --
>>> 1.8.1.2
>>>
>>
>> --
>> Regards,
>> Artem
>>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-12 12:55 ` Peter Hurley
@ 2013-08-12 13:19 ` Sergey Senozhatsky
2013-08-12 13:39 ` Peter Hurley
0 siblings, 1 reply; 7+ messages in thread
From: Sergey Senozhatsky @ 2013-08-12 13:19 UTC (permalink / raw)
To: Peter Hurley
Cc: Greg Kroah-Hartman, linux-next, linux-kernel, Jiri Slaby, Belisko Marek
On (08/12/13 08:55), Peter Hurley wrote:
> >>> [..]
> >>> drivers/tty/n_tty.c | 25 +++++++++++--------------
> >>> 1 file changed, 11 insertions(+), 14 deletions(-)
> >>>
> >
> >I hate to do this, but isn't it actually my patch posted here
> >https://lkml.org/lkml/2013/8/1/510
> >
> >which was tagged as `wrong'?
>
> Sergey,
>
> My apologies; I was mistaken regarding this problem being a lockdep
> regression (although it's still a false positive from lockdep). Once
> I had worked around some issues with the nouveau driver, I was able to
> reproduce the lockdep report on 3.10.
>
no problem.
> I included Artem's lockdep report in the changelog because I received
> that first, on 30 July.
>
> My patch below is not the same as your patch of 1 Aug. This patch
> preserves the protected access of termios.c_cc[VMIN] and termios.c_cc[VTIME]
> (via the MIN_CHAR() and TIME_CHAR() macros).
fair enough. v3 was protecting VMIN/VTIME (my bad, I noticed this a bit later),
but I didn't submit it since v2 did not get positive response.
> If you'd prefer, I could add to changelog:
>
> Patch based on original posted here https://lkml.org/lkml/2013/8/1/510
> by Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
if you don't mind, that would be great.
thanks a lot,
-ss
> Regards,
> Peter Hurley
>
>
> >>>diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> >>>index dd8ae0c..c9a9ddd 100644
> >>>--- a/drivers/tty/n_tty.c
> >>>+++ b/drivers/tty/n_tty.c
> >>>@@ -2122,6 +2122,17 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> >>> if (c < 0)
> >>> return c;
> >>>
> >>>+ /*
> >>>+ * Internal serialization of reads.
> >>>+ */
> >>>+ if (file->f_flags & O_NONBLOCK) {
> >>>+ if (!mutex_trylock(&ldata->atomic_read_lock))
> >>>+ return -EAGAIN;
> >>>+ } else {
> >>>+ if (mutex_lock_interruptible(&ldata->atomic_read_lock))
> >>>+ return -ERESTARTSYS;
> >>>+ }
> >>>+
> >>> down_read(&tty->termios_rwsem);
> >>>
> >>> minimum = time = 0;
> >>>@@ -2141,20 +2152,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> >>> }
> >>> }
> >>>
> >>>- /*
> >>>- * Internal serialization of reads.
> >>>- */
> >>>- if (file->f_flags & O_NONBLOCK) {
> >>>- if (!mutex_trylock(&ldata->atomic_read_lock)) {
> >>>- up_read(&tty->termios_rwsem);
> >>>- return -EAGAIN;
> >>>- }
> >>>- } else {
> >>>- if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
> >>>- up_read(&tty->termios_rwsem);
> >>>- return -ERESTARTSYS;
> >>>- }
> >>>- }
> >>> packet = tty->packet;
> >>>
> >>> add_wait_queue(&tty->read_wait, &wait);
> >>>--
> >>>1.8.1.2
> >>>
> >>
> >>--
> >>Regards,
> >> Artem
> >>
>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-12 13:19 ` Sergey Senozhatsky
@ 2013-08-12 13:39 ` Peter Hurley
2013-08-12 15:53 ` Greg Kroah-Hartman
0 siblings, 1 reply; 7+ messages in thread
From: Peter Hurley @ 2013-08-12 13:39 UTC (permalink / raw)
To: Sergey Senozhatsky, Greg Kroah-Hartman
Cc: linux-next, linux-kernel, Jiri Slaby, Belisko Marek
On 08/12/2013 09:19 AM, Sergey Senozhatsky wrote:
> On (08/12/13 08:55), Peter Hurley wrote:
>>>>> [..]
>>>>> drivers/tty/n_tty.c | 25 +++++++++++--------------
>>>>> 1 file changed, 11 insertions(+), 14 deletions(-)
>>>>>
>>>
>>> I hate to do this, but isn't it actually my patch posted here
>>> https://lkml.org/lkml/2013/8/1/510
>>>
>>> which was tagged as `wrong'?
>>
>> Sergey,
>>
>> My apologies; I was mistaken regarding this problem being a lockdep
>> regression (although it's still a false positive from lockdep). Once
>> I had worked around some issues with the nouveau driver, I was able to
>> reproduce the lockdep report on 3.10.
>>
> no problem.
>
>> I included Artem's lockdep report in the changelog because I received
>> that first, on 30 July.
>>
>> My patch below is not the same as your patch of 1 Aug. This patch
>> preserves the protected access of termios.c_cc[VMIN] and termios.c_cc[VTIME]
>> (via the MIN_CHAR() and TIME_CHAR() macros).
>
> fair enough. v3 was protecting VMIN/VTIME (my bad, I noticed this a bit later),
> but I didn't submit it since v2 did not get positive response.
>
>> If you'd prefer, I could add to changelog:
>>
>> Patch based on original posted here https://lkml.org/lkml/2013/8/1/510
>> by Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
>
> if you don't mind, that would be great.
Ok.
Greg,
Should I re-spin a v2 to include the note above
(or can you add it with Artem's Tested-by)?
Regards,
Peter Hurley
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-08-12 13:39 ` Peter Hurley
@ 2013-08-12 15:53 ` Greg Kroah-Hartman
0 siblings, 0 replies; 7+ messages in thread
From: Greg Kroah-Hartman @ 2013-08-12 15:53 UTC (permalink / raw)
To: Peter Hurley
Cc: Sergey Senozhatsky, linux-next, linux-kernel, Jiri Slaby, Belisko Marek
On Mon, Aug 12, 2013 at 09:39:01AM -0400, Peter Hurley wrote:
> On 08/12/2013 09:19 AM, Sergey Senozhatsky wrote:
> >On (08/12/13 08:55), Peter Hurley wrote:
> >>>>>[..]
> >>>>> drivers/tty/n_tty.c | 25 +++++++++++--------------
> >>>>> 1 file changed, 11 insertions(+), 14 deletions(-)
> >>>>>
> >>>
> >>>I hate to do this, but isn't it actually my patch posted here
> >>>https://lkml.org/lkml/2013/8/1/510
> >>>
> >>>which was tagged as `wrong'?
> >>
> >>Sergey,
> >>
> >>My apologies; I was mistaken regarding this problem being a lockdep
> >>regression (although it's still a false positive from lockdep). Once
> >>I had worked around some issues with the nouveau driver, I was able to
> >>reproduce the lockdep report on 3.10.
> >>
> >no problem.
> >
> >>I included Artem's lockdep report in the changelog because I received
> >>that first, on 30 July.
> >>
> >>My patch below is not the same as your patch of 1 Aug. This patch
> >>preserves the protected access of termios.c_cc[VMIN] and termios.c_cc[VTIME]
> >>(via the MIN_CHAR() and TIME_CHAR() macros).
> >
> >fair enough. v3 was protecting VMIN/VTIME (my bad, I noticed this a bit later),
> >but I didn't submit it since v2 did not get positive response.
> >
> >>If you'd prefer, I could add to changelog:
> >>
> >> Patch based on original posted here https://lkml.org/lkml/2013/8/1/510
> >> by Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> >
> >if you don't mind, that would be great.
>
> Ok.
>
> Greg,
> Should I re-spin a v2 to include the note above
> (or can you add it with Artem's Tested-by)?
I'll add it, no need to resend.
greg k-h
^ permalink raw reply [flat|nested] 7+ messages in thread
end of thread, other threads:[~2013-08-12 15:52 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
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2013-08-11 12:04 ` [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive Peter Hurley
2013-08-12 9:28 ` Artem Savkov
2013-08-12 10:50 ` Sergey Senozhatsky
2013-08-12 12:55 ` Peter Hurley
2013-08-12 13:19 ` Sergey Senozhatsky
2013-08-12 13:39 ` Peter Hurley
2013-08-12 15:53 ` Greg Kroah-Hartman
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