cf872776fc
When a controlling tty is being hung up and the hang up is waiting for a just-signalled tty reader or writer to exit, and a new tty reader/writer tries to acquire an ldisc reference concurrently with the ldisc reference release from the signalled reader/writer, the hangup can hang. The new reader/writer is sleeping in ldsem_down_read() and the hangup is sleeping in ldsem_down_write() [1]. The new reader/writer fails to wakeup the waiting hangup because the wrong lock count value is checked (the old lock count rather than the new lock count) to see if the lock is unowned. Change helper function to return the new lock count if the cmpxchg was successful; document this behavior. [1] edited dmesg log from reporter SysRq : Show Blocked State task PC stack pid father systemd D ffff88040c4f0000 0 1 0 0x00000000 ffff88040c49fbe0 0000000000000046 ffff88040c4a0000 ffff88040c49ffd8 00000000001d3980 00000000001d3980 ffff88040c4a0000 ffff88040593d840 ffff88040c49fb40 ffffffff810a4cc0 0000000000000006 0000000000000023 Call Trace: [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff817a6649>] schedule+0x24/0x5e [<ffffffff817a588b>] schedule_timeout+0x15b/0x1ec [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff817aa691>] ? _raw_spin_unlock_irq+0x24/0x26 [<ffffffff817aa10c>] down_read_failed+0xe3/0x1b9 [<ffffffff817aa26d>] ldsem_down_read+0x8b/0xa5 [<ffffffff8142b5ca>] ? tty_ldisc_ref_wait+0x1b/0x44 [<ffffffff8142b5ca>] tty_ldisc_ref_wait+0x1b/0x44 [<ffffffff81423f5b>] tty_write+0x7d/0x28a [<ffffffff814241f5>] redirected_tty_write+0x8d/0x98 [<ffffffff81424168>] ? tty_write+0x28a/0x28a [<ffffffff8115d03f>] do_loop_readv_writev+0x56/0x79 [<ffffffff8115e604>] do_readv_writev+0x1b0/0x1ff [<ffffffff8116ea0b>] ? do_vfs_ioctl+0x32a/0x489 [<ffffffff81167d9d>] ? final_putname+0x1d/0x3a [<ffffffff8115e6c7>] vfs_writev+0x2e/0x49 [<ffffffff8115e7d3>] SyS_writev+0x47/0xaa [<ffffffff817ab822>] system_call_fastpath+0x16/0x1b bash D ffffffff81c104c0 0 5469 5302 0x00000082 ffff8800cf817ac0 0000000000000046 ffff8804086b22a0 ffff8800cf817fd8 00000000001d3980 00000000001d3980 ffff8804086b22a0 ffff8800cf817a48 000000000000b9a0 ffff8800cf817a78 ffffffff81004675 ffff8800cf817a44 Call Trace: [<ffffffff81004675>] ? dump_trace+0x165/0x29c [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff8100edda>] ? save_stack_trace+0x26/0x41 [<ffffffff817a6649>] schedule+0x24/0x5e [<ffffffff817a588b>] schedule_timeout+0x15b/0x1ec [<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4 [<ffffffff817a9f03>] ? down_write_failed+0xa3/0x1c9 [<ffffffff817aa691>] ? _raw_spin_unlock_irq+0x24/0x26 [<ffffffff817a9f0b>] down_write_failed+0xab/0x1c9 [<ffffffff817aa300>] ldsem_down_write+0x79/0xb1 [<ffffffff817aada3>] ? tty_ldisc_lock_pair_timeout+0xa5/0xd9 [<ffffffff817aada3>] tty_ldisc_lock_pair_timeout+0xa5/0xd9 [<ffffffff8142bf33>] tty_ldisc_hangup+0xc4/0x218 [<ffffffff81423ab3>] __tty_hangup+0x2e2/0x3ed [<ffffffff81424a76>] disassociate_ctty+0x63/0x226 [<ffffffff81078aa7>] do_exit+0x79f/0xa11 [<ffffffff81086bdb>] ? get_signal_to_deliver+0x206/0x62f [<ffffffff810b4bfb>] ? lock_release_holdtime.part.8+0xf/0x16e [<ffffffff81079b05>] do_group_exit+0x47/0xb5 [<ffffffff81086c16>] get_signal_to_deliver+0x241/0x62f [<ffffffff810020a7>] do_signal+0x43/0x59d [<ffffffff810f2af7>] ? __audit_syscall_exit+0x21a/0x2a8 [<ffffffff810b4bfb>] ? lock_release_holdtime.part.8+0xf/0x16e [<ffffffff81002655>] do_notify_resume+0x54/0x6c [<ffffffff817abaf8>] int_signal+0x12/0x17 Reported-by: Sami Farin <sami.farin@gmail.com> Cc: <stable@vger.kernel.org> # 3.12.x Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
||
|---|---|---|
| .. | ||
| hvc | ||
| ipwireless | ||
| serial | ||
| vt | ||
| amiserial.c | ||
| bfin_jtag_comm.c | ||
| cyclades.c | ||
| ehv_bytechan.c | ||
| goldfish.c | ||
| isicom.c | ||
| Kconfig | ||
| Makefile | ||
| metag_da.c | ||
| moxa.c | ||
| moxa.h | ||
| mxser.c | ||
| mxser.h | ||
| n_gsm.c | ||
| n_hdlc.c | ||
| n_r3964.c | ||
| n_tracerouter.c | ||
| n_tracesink.c | ||
| n_tracesink.h | ||
| n_tty.c | ||
| nozomi.c | ||
| pty.c | ||
| rocket_int.h | ||
| rocket.c | ||
| rocket.h | ||
| synclink_gt.c | ||
| synclink.c | ||
| synclinkmp.c | ||
| sysrq.c | ||
| tty_audit.c | ||
| tty_buffer.c | ||
| tty_io.c | ||
| tty_ioctl.c | ||
| tty_ldisc.c | ||
| tty_ldsem.c | ||
| tty_mutex.c | ||
| tty_port.c | ||