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 <[email protected]> > Reported-by: Artem Savkov <[email protected]> > Reported-by: Sergey Senozhatsky <[email protected]> > Signed-off-by: Peter Hurley <[email protected]> > > [1] Initial lockdep report from Artem Savkov <[email protected]> > > ====================================================== > [ 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
