Message ID | 200901131004.22609.borntraeger@de.ibm.com (mailing list archive) |
---|---|
State | Not Applicable, archived |
Headers | show |
Am Dienstag 13 Januar 2009 schrieb Christian Borntraeger: > drivers/char/hvc_console.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > Index: linux-2.6/drivers/char/hvc_console.c > =================================================================== > --- linux-2.6.orig/drivers/char/hvc_console.c > +++ linux-2.6/drivers/char/hvc_console.c > @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t > } /* else count == 0 */ > > tty->driver_data = hp; > - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > - > hp->tty = tty; > > spin_unlock_irqrestore(&hp->lock, flags); > @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t > if (hp->ops->notifier_add) > rc = hp->ops->notifier_add(hp, hp->data); > > + if (!hp->irq_requested) > + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > + > /* > * If the notifier fails we return an error. The tty layer > * will call hvc_close() after a failed open but we don't want to clean > > Just in case: Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Here is yet another bug trace related to the low_latency issue, that is experienced using the hvc_iucv backend. The hvc_iucv backend now also uses irq notifiers. The bug trace below appears if hvc_kick() is called. On Tue, Jan 13, 2009 at 10:04:22AM +0100, Christian Borntraeger wrote: > Am Donnerstag 08 Januar 2009 schrieb Milton Miller: > > hvc_console is setting low_latency unconditionally, but some clients are > > interrupt driven and will call hvc_poll from irq context. This will cause > > tty_flip_buffer_push to be called from irq context, and it very clearly > > states it must not be called from IRQ when low_latency is specified. It seems that if low_latency is set, tty_flip_buffer_push() should also not be called within an atomic context, because echo_char_raw() and other echo* calls might sleep. Christian's patch solves this problem for irq driven backends. However, there might be still a problem with polled backends since the khvcd() thread calls hvc_poll() while hvc_structs_lock is held. I think the hvc_udbg backend is based on polling. David, could you check if you experience any problems with your hvc_udbg backend on latest git. BUG: sleeping function called from invalid context at /root/cvs/linux-2.6.git/kernel/mutex.c:207 in_atomic(): 1, irqs_disabled(): 0, pid: 748, name: khvcd 1 lock held by khvcd/748: #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] khvcd+0x58/0x12c CPU: 0 Not tainted 2.6.29-rc1git #29 Process khvcd (pid: 748, task: 000000002fb9a480, ksp: 000000002f66bd78) 070000000000000a 000000002f66ba00 0000000000000002 (null) 000000002f66baa0 000000002f66ba18 000000002f66ba18 0000000000104f08 ffffffffffffc000 000000002f66bd78 (null) (null) 000000002f66ba00 000000000000000c 000000002f66ba00 000000002f66ba70 0000000000466af8 0000000000104f08 000000002f66ba00 000000002f66ba50 Call Trace: ([<0000000000104e7c>] show_trace+0x138/0x158) [<0000000000104f62>] show_stack+0xc6/0xf8 [<0000000000105740>] dump_stack+0xb0/0xc0 [<000000000013144a>] __might_sleep+0x14e/0x17c [<000000000045e226>] mutex_lock_nested+0x42/0x3b4 [<00000000002c443e>] echo_char_raw+0x3a/0x9c [<00000000002c688c>] n_tty_receive_buf+0x1154/0x1208 [<00000000002ca0a2>] flush_to_ldisc+0x152/0x220 [<00000000002ca1da>] tty_flip_buffer_push+0x6a/0x90 [<00000000002cea74>] hvc_poll+0x244/0x2c8 [<00000000002ceb68>] khvcd+0x70/0x12c [<000000000015bbd0>] kthread+0x68/0xa0 [<0000000000109d5a>] kernel_thread_starter+0x6/0xc [<0000000000109d54>] kernel_thread_starter+0x0/0xc 1 lock held by khvcd/748: #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] khvcd+0x58/0x12c > This wont work, since the call to notifier_add is done later: > What about: > --- > drivers/char/hvc_console.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > Index: linux-2.6/drivers/char/hvc_console.c > =================================================================== > --- linux-2.6.orig/drivers/char/hvc_console.c > +++ linux-2.6/drivers/char/hvc_console.c > @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t > } /* else count == 0 */ > > tty->driver_data = hp; > - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > - > hp->tty = tty; > > spin_unlock_irqrestore(&hp->lock, flags); > @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t > if (hp->ops->notifier_add) > rc = hp->ops->notifier_add(hp, hp->data); > > + if (!hp->irq_requested) > + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > + > /* > * If the notifier fails we return an error. The tty layer > * will call hvc_close() after a failed open but we don't want to clean Acked-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
On Jan 13, 2009, at 5:35 AM, Hendrik Brueckner wrote: > Here is yet another bug trace related to the low_latency issue, that is > experienced using the hvc_iucv backend. The hvc_iucv backend now also > uses irq > notifiers. > The bug trace below appears if hvc_kick() is called. > > On Tue, Jan 13, 2009 at 10:04:22AM +0100, Christian Borntraeger wrote: >> Am Donnerstag 08 Januar 2009 schrieb Milton Miller: >>> hvc_console is setting low_latency unconditionally, but some clients >>> are >>> interrupt driven and will call hvc_poll from irq context. This will >>> cause >>> tty_flip_buffer_push to be called from irq context, and it very >>> clearly >>> states it must not be called from IRQ when low_latency is specified. > It seems that if low_latency is set, tty_flip_buffer_push() should > also not be > called within an atomic context, because echo_char_raw() and other > echo* calls > might sleep. > > Christian's patch solves this problem for irq driven backends. > However, there might be still a problem with polled backends since the > khvcd() > thread calls hvc_poll() while hvc_structs_lock is held. > > I think the hvc_udbg backend is based on polling. > David, could you check if you experience any problems with your > hvc_udbg > backend on latest git. > So the simplest is to never set it. milton > BUG: sleeping function called from invalid context at > /root/cvs/linux-2.6.git/kernel/mutex.c:207 > in_atomic(): 1, irqs_disabled(): 0, pid: 748, name: khvcd > 1 lock held by khvcd/748: > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > khvcd+0x58/0x12c > CPU: 0 Not tainted 2.6.29-rc1git #29 > Process khvcd (pid: 748, task: 000000002fb9a480, ksp: 000000002f66bd78) > 070000000000000a 000000002f66ba00 0000000000000002 (null) > 000000002f66baa0 000000002f66ba18 000000002f66ba18 > 0000000000104f08 > ffffffffffffc000 000000002f66bd78 (null) (null) > 000000002f66ba00 000000000000000c 000000002f66ba00 > 000000002f66ba70 > 0000000000466af8 0000000000104f08 000000002f66ba00 > 000000002f66ba50 > Call Trace: > ([<0000000000104e7c>] show_trace+0x138/0x158) > [<0000000000104f62>] show_stack+0xc6/0xf8 > [<0000000000105740>] dump_stack+0xb0/0xc0 > [<000000000013144a>] __might_sleep+0x14e/0x17c > [<000000000045e226>] mutex_lock_nested+0x42/0x3b4 > [<00000000002c443e>] echo_char_raw+0x3a/0x9c > [<00000000002c688c>] n_tty_receive_buf+0x1154/0x1208 > [<00000000002ca0a2>] flush_to_ldisc+0x152/0x220 > [<00000000002ca1da>] tty_flip_buffer_push+0x6a/0x90 > [<00000000002cea74>] hvc_poll+0x244/0x2c8 > [<00000000002ceb68>] khvcd+0x70/0x12c > [<000000000015bbd0>] kthread+0x68/0xa0 > [<0000000000109d5a>] kernel_thread_starter+0x6/0xc > [<0000000000109d54>] kernel_thread_starter+0x0/0xc > 1 lock held by khvcd/748: > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > khvcd+0x58/0x12c > >> This wont work, since the call to notifier_add is done later: >> What about: >> --- >> drivers/char/hvc_console.c | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> Index: linux-2.6/drivers/char/hvc_console.c >> =================================================================== >> --- linux-2.6.orig/drivers/char/hvc_console.c >> +++ linux-2.6/drivers/char/hvc_console.c >> @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t >> } /* else count == 0 */ >> >> tty->driver_data = hp; >> - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ >> - >> hp->tty = tty; >> >> spin_unlock_irqrestore(&hp->lock, flags); >> @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t >> if (hp->ops->notifier_add) >> rc = hp->ops->notifier_add(hp, hp->data); >> >> + if (!hp->irq_requested) >> + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ >> + >> /* >> * If the notifier fails we return an error. The tty layer >> * will call hvc_close() after a failed open but we don't want to >> clean > > Acked-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com> >
> So the simplest is to never set it. I already applied your previous patch. Please send an incremental fix. Cheers, Ben. > milton > > > BUG: sleeping function called from invalid context at > > /root/cvs/linux-2.6.git/kernel/mutex.c:207 > > in_atomic(): 1, irqs_disabled(): 0, pid: 748, name: khvcd > > 1 lock held by khvcd/748: > > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > > khvcd+0x58/0x12c > > CPU: 0 Not tainted 2.6.29-rc1git #29 > > Process khvcd (pid: 748, task: 000000002fb9a480, ksp: 000000002f66bd78) > > 070000000000000a 000000002f66ba00 0000000000000002 (null) > > 000000002f66baa0 000000002f66ba18 000000002f66ba18 > > 0000000000104f08 > > ffffffffffffc000 000000002f66bd78 (null) (null) > > 000000002f66ba00 000000000000000c 000000002f66ba00 > > 000000002f66ba70 > > 0000000000466af8 0000000000104f08 000000002f66ba00 > > 000000002f66ba50 > > Call Trace: > > ([<0000000000104e7c>] show_trace+0x138/0x158) > > [<0000000000104f62>] show_stack+0xc6/0xf8 > > [<0000000000105740>] dump_stack+0xb0/0xc0 > > [<000000000013144a>] __might_sleep+0x14e/0x17c > > [<000000000045e226>] mutex_lock_nested+0x42/0x3b4 > > [<00000000002c443e>] echo_char_raw+0x3a/0x9c > > [<00000000002c688c>] n_tty_receive_buf+0x1154/0x1208 > > [<00000000002ca0a2>] flush_to_ldisc+0x152/0x220 > > [<00000000002ca1da>] tty_flip_buffer_push+0x6a/0x90 > > [<00000000002cea74>] hvc_poll+0x244/0x2c8 > > [<00000000002ceb68>] khvcd+0x70/0x12c > > [<000000000015bbd0>] kthread+0x68/0xa0 > > [<0000000000109d5a>] kernel_thread_starter+0x6/0xc > > [<0000000000109d54>] kernel_thread_starter+0x0/0xc > > 1 lock held by khvcd/748: > > #0: (hvc_structs_lock){--..}, at: [<00000000002ceb50>] > > khvcd+0x58/0x12c > > > >> This wont work, since the call to notifier_add is done later: > >> What about: > >> --- > >> drivers/char/hvc_console.c | 5 +++-- > >> 1 file changed, 3 insertions(+), 2 deletions(-) > >> > >> Index: linux-2.6/drivers/char/hvc_console.c > >> =================================================================== > >> --- linux-2.6.orig/drivers/char/hvc_console.c > >> +++ linux-2.6/drivers/char/hvc_console.c > >> @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t > >> } /* else count == 0 */ > >> > >> tty->driver_data = hp; > >> - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > >> - > >> hp->tty = tty; > >> > >> spin_unlock_irqrestore(&hp->lock, flags); > >> @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t > >> if (hp->ops->notifier_add) > >> rc = hp->ops->notifier_add(hp, hp->data); > >> > >> + if (!hp->irq_requested) > >> + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ > >> + > >> /* > >> * If the notifier fails we return an error. The tty layer > >> * will call hvc_close() after a failed open but we don't want to > >> clean > > > > Acked-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com> > >
Index: linux-2.6/drivers/char/hvc_console.c =================================================================== --- linux-2.6.orig/drivers/char/hvc_console.c +++ linux-2.6/drivers/char/hvc_console.c @@ -318,8 +318,6 @@ static int hvc_open(struct tty_struct *t } /* else count == 0 */ tty->driver_data = hp; - tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ - hp->tty = tty; spin_unlock_irqrestore(&hp->lock, flags); @@ -327,6 +325,9 @@ static int hvc_open(struct tty_struct *t if (hp->ops->notifier_add) rc = hp->ops->notifier_add(hp, hp->data); + if (!hp->irq_requested) + tty->low_latency = 1; /* Makes flushes to ldisc synchronous. */ + /* * If the notifier fails we return an error. The tty layer * will call hvc_close() after a failed open but we don't want to clean