* [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout()
@ 2013-07-30 15:35 Artem Savkov
2013-07-30 16:39 ` Peter Hurley
0 siblings, 1 reply; 11+ messages in thread
From: Artem Savkov @ 2013-07-30 15:35 UTC (permalink / raw)
To: peter; +Cc: gregkh, jslaby, linux-kernel, Artem Savkov
ldata->atomic_read_lock should be released before scheduling as well as
tty->termios_rwsem, otherwise there is a potential deadlock detected by lockdep
Introduced in "n_tty: Access termios values safely"
(9356b535fcb71db494fc434acceb79f56d15bda2 in linux-next.git)
[ 16.822058] ======================================================
[ 16.822058] [ INFO: possible circular locking dependency detected ]
[ 16.822058] 3.11.0-rc3-next-20130730+ #140 Tainted: G W
[ 16.822058] -------------------------------------------------------
[ 16.822058] bash/1198 is trying to acquire lock:
[ 16.822058] (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
[ 16.822058]
[ 16.822058] but task is already holding lock:
[ 16.822058] (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
[ 16.822058]
[ 16.822058] which lock already depends on the new lock.
[ 16.822058]
[ 16.822058]
[ 16.822058] the existing dependency chain (in reverse order) is:
[ 16.822058]
-> #1 (&ldata->atomic_read_lock){+.+...}:
[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[ 16.822058] [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
[ 16.822058] [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
[ 16.822058]
-> #0 (&tty->termios_rwsem){++++..}:
[ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
[ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
[ 16.822058]
[ 16.822058] other info that might help us debug this:
[ 16.822058]
[ 16.822058] Possible unsafe locking scenario:
[ 16.822058]
[ 16.822058] CPU0 CPU1
[ 16.822058] ---- ----
[ 16.822058] lock(&ldata->atomic_read_lock);
[ 16.822058] lock(&tty->termios_rwsem);
[ 16.822058] lock(&ldata->atomic_read_lock);
[ 16.822058] lock(&tty->termios_rwsem);
[ 16.822058]
[ 16.822058] *** DEADLOCK ***
[ 16.822058]
[ 16.822058] 2 locks held by bash/1198:
[ 16.822058] #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
[ 16.822058] #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
[ 16.822058]
[ 16.822058] stack backtrace:
[ 16.822058] CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
[ 16.822058] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
[ 16.822058] 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
[ 16.822058] 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
[ 16.822058] ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
[ 16.822058] Call Trace:
[ 16.822058] [<ffffffff81d34074>] dump_stack+0x59/0x7d
[ 16.822058] [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
[ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
[ 16.822058] [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
[ 16.822058] [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
[ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
[ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
[ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
[ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
[ 16.822058] [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
[ 16.822058] [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
Signed-off-by: Artem Savkov <artem.savkov@gmail.com>
---
drivers/tty/n_tty.c | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index dd8ae0c..38c09db 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -2203,11 +2203,23 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
break;
}
n_tty_set_room(tty);
+ mutex_unlock(&ldata->atomic_read_lock);
up_read(&tty->termios_rwsem);
timeout = schedule_timeout(timeout);
down_read(&tty->termios_rwsem);
+ if (file->f_flags & O_NONBLOCK) {
+ if (!mutex_trylock(&ldata->atomic_read_lock)) {
+ retval = -EAGAIN;
+ break;
+ }
+ } else {
+ if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
+ retval = -ERESTARTSYS;
+ break;
+ }
+ }
continue;
}
__set_current_state(TASK_RUNNING);
--
1.7.0.4
^ permalink raw reply related [flat|nested] 11+ messages in thread
* Re: [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout()
2013-07-30 15:35 [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout() Artem Savkov
@ 2013-07-30 16:39 ` Peter Hurley
2013-07-31 11:47 ` Artem Savkov
0 siblings, 1 reply; 11+ messages in thread
From: Peter Hurley @ 2013-07-30 16:39 UTC (permalink / raw)
To: Artem Savkov, Michel Lespinasse; +Cc: gregkh, jslaby, linux-kernel, Ingo Molnar
On 07/30/2013 11:35 AM, Artem Savkov wrote:
> ldata->atomic_read_lock should be released before scheduling as well as
> tty->termios_rwsem, otherwise there is a potential deadlock detected by lockdep
False positive.
> Introduced in "n_tty: Access termios values safely"
> (9356b535fcb71db494fc434acceb79f56d15bda2 in linux-next.git)
>
> [ 16.822058] ======================================================
> [ 16.822058] [ INFO: possible circular locking dependency detected ]
> [ 16.822058] 3.11.0-rc3-next-20130730+ #140 Tainted: G W
> [ 16.822058] -------------------------------------------------------
> [ 16.822058] bash/1198 is trying to acquire lock:
> [ 16.822058] (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> [ 16.822058]
> [ 16.822058] but task is already holding lock:
> [ 16.822058] (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> [ 16.822058]
> [ 16.822058] which lock already depends on the new lock.
> [ 16.822058]
> [ 16.822058]
> [ 16.822058] the existing dependency chain (in reverse order) is:
> [ 16.822058]
> -> #1 (&ldata->atomic_read_lock){+.+...}:
> [ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [ 16.822058] [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
> [ 16.822058] [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> [ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> [ 16.822058]
> -> #0 (&tty->termios_rwsem){++++..}:
> [ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> [ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
> [ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> [ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> [ 16.822058]
> [ 16.822058] other info that might help us debug this:
> [ 16.822058]
> [ 16.822058] Possible unsafe locking scenario:
> [ 16.822058]
> [ 16.822058] CPU0 CPU1
> [ 16.822058] ---- ----
> [ 16.822058] lock(&ldata->atomic_read_lock);
> [ 16.822058] lock(&tty->termios_rwsem);
> [ 16.822058] lock(&ldata->atomic_read_lock);
> [ 16.822058] lock(&tty->termios_rwsem);
> [ 16.822058]
> [ 16.822058] *** DEADLOCK ***
This situation is not possible since termios_rwsem is a read/write semaphore;
CPU1 cannot prevent CPU0 from obtaining a read lock on termios_rwsem.
This looks like a regression caused by:
commit a51805efae5dda0da66f79268ffcf0715f9dbea4
Author: Michel Lespinasse <walken@google.com>
Date: Mon Jul 8 14:23:49 2013 -0700
lockdep: Introduce lock_acquire_exclusive()/shared() helper macros
In lockdep.h, the spinlock/mutex/rwsem/rwlock/lock_map acquire macros have
different definitions based on the value of CONFIG_PROVE_LOCKING. We have
separate ifdefs for each of these definitions, which seems redundant.
Introduce lock_acquire_{exclusive,shared,shared_recursive} helpers which
will have different definitions based on CONFIG_PROVE_LOCKING. Then all
other helper macros can be defined based on the above ones, which reduces
the amount of ifdefined code.
Signed-off-by: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20130708212350.6DD1931C15E@corp2gmr1-1.hot.corp.google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
> [ 16.822058]
> [ 16.822058] 2 locks held by bash/1198:
> [ 16.822058] #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
> [ 16.822058] #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> [ 16.822058]
> [ 16.822058] stack backtrace:
> [ 16.822058] CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
> [ 16.822058] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> [ 16.822058] 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
> [ 16.822058] 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
> [ 16.822058] ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
> [ 16.822058] Call Trace:
> [ 16.822058] [<ffffffff81d34074>] dump_stack+0x59/0x7d
> [ 16.822058] [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
> [ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> [ 16.822058] [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
> [ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> [ 16.822058] [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
> [ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> [ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> [ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> [ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
> [ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> [ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> [ 16.822058] [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
> [ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> [ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> [ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> [ 16.822058] [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> [ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>
> Signed-off-by: Artem Savkov <artem.savkov@gmail.com>
> ---
> drivers/tty/n_tty.c | 12 ++++++++++++
> 1 files changed, 12 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> index dd8ae0c..38c09db 100644
> --- a/drivers/tty/n_tty.c
> +++ b/drivers/tty/n_tty.c
> @@ -2203,11 +2203,23 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> break;
> }
> n_tty_set_room(tty);
> + mutex_unlock(&ldata->atomic_read_lock);
> up_read(&tty->termios_rwsem);
>
> timeout = schedule_timeout(timeout);
>
> down_read(&tty->termios_rwsem);
> + if (file->f_flags & O_NONBLOCK) {
> + if (!mutex_trylock(&ldata->atomic_read_lock)) {
> + retval = -EAGAIN;
> + break;
> + }
> + } else {
> + if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
> + retval = -ERESTARTSYS;
> + break;
> + }
> + }
> continue;
> }
> __set_current_state(TASK_RUNNING);
>
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout()
2013-07-30 16:39 ` Peter Hurley
@ 2013-07-31 11:47 ` Artem Savkov
2013-08-01 20:06 ` Peter Hurley
2013-08-11 12:04 ` [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive Peter Hurley
0 siblings, 2 replies; 11+ messages in thread
From: Artem Savkov @ 2013-07-31 11:47 UTC (permalink / raw)
To: Peter Hurley; +Cc: Michel Lespinasse, gregkh, jslaby, linux-kernel, Ingo Molnar
On Tue, Jul 30, 2013 at 12:39:54PM -0400, Peter Hurley wrote:
> On 07/30/2013 11:35 AM, Artem Savkov wrote:
> >ldata->atomic_read_lock should be released before scheduling as well as
> >tty->termios_rwsem, otherwise there is a potential deadlock detected by lockdep
>
> False positive.
>
> >Introduced in "n_tty: Access termios values safely"
> >(9356b535fcb71db494fc434acceb79f56d15bda2 in linux-next.git)
> >
> >[ 16.822058] ======================================================
> >[ 16.822058] [ INFO: possible circular locking dependency detected ]
> >[ 16.822058] 3.11.0-rc3-next-20130730+ #140 Tainted: G W
> >[ 16.822058] -------------------------------------------------------
> >[ 16.822058] bash/1198 is trying to acquire lock:
> >[ 16.822058] (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> >[ 16.822058]
> >[ 16.822058] but task is already holding lock:
> >[ 16.822058] (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> >[ 16.822058]
> >[ 16.822058] which lock already depends on the new lock.
> >[ 16.822058]
> >[ 16.822058]
> >[ 16.822058] the existing dependency chain (in reverse order) is:
> >[ 16.822058]
> >-> #1 (&ldata->atomic_read_lock){+.+...}:
> >[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> >[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> >[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> >[ 16.822058] [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
> >[ 16.822058] [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> >[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> >[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> >[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> >[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> >[ 16.822058]
> >-> #0 (&tty->termios_rwsem){++++..}:
> >[ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> >[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> >[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> >[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> >[ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
> >[ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> >[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> >[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> >[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> >[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> >[ 16.822058]
> >[ 16.822058] other info that might help us debug this:
> >[ 16.822058]
> >[ 16.822058] Possible unsafe locking scenario:
> >[ 16.822058]
> >[ 16.822058] CPU0 CPU1
> >[ 16.822058] ---- ----
> >[ 16.822058] lock(&ldata->atomic_read_lock);
> >[ 16.822058] lock(&tty->termios_rwsem);
> >[ 16.822058] lock(&ldata->atomic_read_lock);
> >[ 16.822058] lock(&tty->termios_rwsem);
> >[ 16.822058]
> >[ 16.822058] *** DEADLOCK ***
>
> This situation is not possible since termios_rwsem is a read/write semaphore;
> CPU1 cannot prevent CPU0 from obtaining a read lock on termios_rwsem.
Oops, yes, sorry.
> This looks like a regression caused by:
>
> commit a51805efae5dda0da66f79268ffcf0715f9dbea4
> Author: Michel Lespinasse <walken@google.com>
> Date: Mon Jul 8 14:23:49 2013 -0700
>
> lockdep: Introduce lock_acquire_exclusive()/shared() helper macros
Doesn't seem to be this commit. I see nothing wrong here and just to be
sure I've checked the kernel with this commit reverted. The issue is
still there.
> In lockdep.h, the spinlock/mutex/rwsem/rwlock/lock_map acquire macros have
> different definitions based on the value of CONFIG_PROVE_LOCKING. We have
> separate ifdefs for each of these definitions, which seems redundant.
>
> Introduce lock_acquire_{exclusive,shared,shared_recursive} helpers which
> will have different definitions based on CONFIG_PROVE_LOCKING. Then all
> other helper macros can be defined based on the above ones, which reduces
> the amount of ifdefined code.
>
> Signed-off-by: Michel Lespinasse <walken@google.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Peter Zijlstra <peterz@infradead.org>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
> Cc: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
> Cc: Rusty Russell <rusty@rustcorp.com.au>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Link: http://lkml.kernel.org/r/20130708212350.6DD1931C15E@corp2gmr1-1.hot.corp.google.com
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
>
>
> >[ 16.822058]
> >[ 16.822058] 2 locks held by bash/1198:
> >[ 16.822058] #0: (&tty->ldisc_sem){.+.+.+}, at: [<ffffffff816ade04>] tty_ldisc_ref_wait+0x24/0x60
> >[ 16.822058] #1: (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
> >[ 16.822058]
> >[ 16.822058] stack backtrace:
> >[ 16.822058] CPU: 1 PID: 1198 Comm: bash Tainted: G W 3.11.0-rc3-next-20130730+ #140
> >[ 16.822058] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
> >[ 16.822058] 0000000000000000 ffff880019acdb28 ffffffff81d34074 0000000000000002
> >[ 16.822058] 0000000000000000 ffff880019acdb78 ffffffff8110ed75 ffff880019acdb98
> >[ 16.822058] ffff880019fd0000 ffff880019acdb78 ffff880019fd0638 ffff880019fd0670
> >[ 16.822058] Call Trace:
> >[ 16.822058] [<ffffffff81d34074>] dump_stack+0x59/0x7d
> >[ 16.822058] [<ffffffff8110ed75>] print_circular_bug+0x105/0x120
> >[ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
> >[ 16.822058] [<ffffffff81d3ab5f>] ? _raw_spin_unlock_irq+0x4f/0x70
> >[ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
> >[ 16.822058] [<ffffffff8110ae0f>] ? trace_hardirqs_off_caller+0x1f/0x190
> >[ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
> >[ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
> >[ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> >[ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
> >[ 16.822058] [<ffffffff816aa3bb>] ? n_tty_read+0x49b/0x660
> >[ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
> >[ 16.822058] [<ffffffff810e4130>] ? try_to_wake_up+0x210/0x210
> >[ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
> >[ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
> >[ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
> >[ 16.822058] [<ffffffff815e24ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
> >[ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
> >
> >Signed-off-by: Artem Savkov <artem.savkov@gmail.com>
> >---
> > drivers/tty/n_tty.c | 12 ++++++++++++
> > 1 files changed, 12 insertions(+), 0 deletions(-)
> >
> >diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
> >index dd8ae0c..38c09db 100644
> >--- a/drivers/tty/n_tty.c
> >+++ b/drivers/tty/n_tty.c
> >@@ -2203,11 +2203,23 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
> > break;
> > }
> > n_tty_set_room(tty);
> >+ mutex_unlock(&ldata->atomic_read_lock);
> > up_read(&tty->termios_rwsem);
> >
> > timeout = schedule_timeout(timeout);
> >
> > down_read(&tty->termios_rwsem);
> >+ if (file->f_flags & O_NONBLOCK) {
> >+ if (!mutex_trylock(&ldata->atomic_read_lock)) {
> >+ retval = -EAGAIN;
> >+ break;
> >+ }
> >+ } else {
> >+ if (mutex_lock_interruptible(&ldata->atomic_read_lock)) {
> >+ retval = -ERESTARTSYS;
> >+ break;
> >+ }
> >+ }
> > continue;
> > }
> > __set_current_state(TASK_RUNNING);
> >
>
--
Regards,
Artem
^ permalink raw reply [flat|nested] 11+ messages in thread
* Re: [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout()
2013-07-31 11:47 ` Artem Savkov
@ 2013-08-01 20:06 ` Peter Hurley
2013-08-11 12:04 ` [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive Peter Hurley
1 sibling, 0 replies; 11+ messages in thread
From: Peter Hurley @ 2013-08-01 20:06 UTC (permalink / raw)
To: Michel Lespinasse, Artem Savkov; +Cc: gregkh, jslaby, linux-kernel, Ingo Molnar
On 07/31/2013 07:47 AM, Artem Savkov wrote:
> On Tue, Jul 30, 2013 at 12:39:54PM -0400, Peter Hurley wrote:
>> On 07/30/2013 11:35 AM, Artem Savkov wrote:
>>> ldata->atomic_read_lock should be released before scheduling as well as
>>> tty->termios_rwsem, otherwise there is a potential deadlock detected by lockdep
>>
>> False positive.
>>
>>> Introduced in "n_tty: Access termios values safely"
>>> (9356b535fcb71db494fc434acceb79f56d15bda2 in linux-next.git)
>>>
>>> [ 16.822058] ======================================================
>>> [ 16.822058] [ INFO: possible circular locking dependency detected ]
>>> [ 16.822058] 3.11.0-rc3-next-20130730+ #140 Tainted: G W
>>> [ 16.822058] -------------------------------------------------------
>>> [ 16.822058] bash/1198 is trying to acquire lock:
>>> [ 16.822058] (&tty->termios_rwsem){++++..}, at: [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>>> [ 16.822058]
>>> [ 16.822058] but task is already holding lock:
>>> [ 16.822058] (&ldata->atomic_read_lock){+.+...}, at: [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>>> [ 16.822058]
>>> [ 16.822058] which lock already depends on the new lock.
>>> [ 16.822058]
>>> [ 16.822058]
>>> [ 16.822058] the existing dependency chain (in reverse order) is:
>>> [ 16.822058]
>>> -> #1 (&ldata->atomic_read_lock){+.+...}:
>>> [ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
>>> [ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
>>> [ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
>>> [ 16.822058] [<ffffffff81d34b9c>] mutex_lock_interruptible_nested+0x7c/0x540
>>> [ 16.822058] [<ffffffff816aa0f0>] n_tty_read+0x1d0/0x660
>>> [ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
>>> [ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
>>> [ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
>>> [ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>>> [ 16.822058]
>>> -> #0 (&tty->termios_rwsem){++++..}:
>>> [ 16.822058] [<ffffffff8111064f>] check_prev_add+0x14f/0x590
>>> [ 16.822058] [<ffffffff811111cc>] validate_chain+0x73c/0x850
>>> [ 16.822058] [<ffffffff811117e0>] __lock_acquire+0x500/0x5d0
>>> [ 16.822058] [<ffffffff81111a29>] lock_acquire+0x179/0x1d0
>>> [ 16.822058] [<ffffffff81d372c1>] down_read+0x51/0xa0
>>> [ 16.822058] [<ffffffff816aa3bb>] n_tty_read+0x49b/0x660
>>> [ 16.822058] [<ffffffff816a3bb6>] tty_read+0x86/0xf0
>>> [ 16.822058] [<ffffffff811f21d3>] vfs_read+0xc3/0x130
>>> [ 16.822058] [<ffffffff811f2702>] SyS_read+0x62/0xa0
>>> [ 16.822058] [<ffffffff81d45259>] system_call_fastpath+0x16/0x1b
>>> [ 16.822058]
>>> [ 16.822058] other info that might help us debug this:
>>> [ 16.822058]
>>> [ 16.822058] Possible unsafe locking scenario:
>>> [ 16.822058]
>>> [ 16.822058] CPU0 CPU1
>>> [ 16.822058] ---- ----
>>> [ 16.822058] lock(&ldata->atomic_read_lock);
>>> [ 16.822058] lock(&tty->termios_rwsem);
>>> [ 16.822058] lock(&ldata->atomic_read_lock);
>>> [ 16.822058] lock(&tty->termios_rwsem);
>>> [ 16.822058]
>>> [ 16.822058] *** DEADLOCK ***
>>
>> This situation is not possible since termios_rwsem is a read/write semaphore;
>> CPU1 cannot prevent CPU0 from obtaining a read lock on termios_rwsem.
> Oops, yes, sorry.
>
>> This looks like a regression caused by:
>>
>> commit a51805efae5dda0da66f79268ffcf0715f9dbea4
>> Author: Michel Lespinasse <walken@google.com>
>> Date: Mon Jul 8 14:23:49 2013 -0700
>>
>> lockdep: Introduce lock_acquire_exclusive()/shared() helper macros
> Doesn't seem to be this commit. I see nothing wrong here and just to be
> sure I've checked the kernel with this commit reverted. The issue is
> still there.
Yes, you're right. Apologies to Michel for the too-hasty blame.
Thanks for the report anyway. I'll track down the lockdep regression
as soon as I fix a real deadlock in the nouveau driver that disables
lockdep.
Regards,
Peter Hurley
^ permalink raw reply [flat|nested] 11+ messages in thread
* [PATCH tty-next] n_tty: Fix termios_rwsem lockdep false positive
2013-07-31 11:47 ` Artem Savkov
2013-08-01 20:06 ` Peter Hurley
@ 2013-08-11 12:04 ` Peter Hurley
2013-08-12 9:28 ` Artem Savkov
1 sibling, 1 reply; 11+ 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] 11+ 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; 11+ 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] 11+ 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; 11+ 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] 11+ 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; 11+ 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] 11+ 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; 11+ 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] 11+ 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; 11+ 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] 11+ 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; 11+ 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] 11+ messages in thread
end of thread, other threads:[~2013-08-12 15:52 UTC | newest]
Thread overview: 11+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-07-30 15:35 [PATCH] n_tty: release atomic_read_lock before calling schedule_timeout() Artem Savkov
2013-07-30 16:39 ` Peter Hurley
2013-07-31 11:47 ` Artem Savkov
2013-08-01 20:06 ` Peter Hurley
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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