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aefceaf453
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. Patch based on original posted here https://lkml.org/lkml/2013/8/1/510 by Sergey Senozhatsky <sergey.senozhatsky@gmail.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 Reported-by: Artem Savkov <artem.savkov@gmail.com> Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
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