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122 lines
5.0 KiB
Diff
122 lines
5.0 KiB
Diff
From cf872776fc84128bb779ce2b83a37c884c3203ae Mon Sep 17 00:00:00 2001
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From: Peter Hurley <peter@hurleysoftware.com>
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Date: Wed, 11 Dec 2013 21:11:58 -0500
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Subject: tty: Fix hang at ldsem_down_read()
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When a controlling tty is being hung up and the hang up is
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waiting for a just-signalled tty reader or writer to exit, and a new tty
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reader/writer tries to acquire an ldisc reference concurrently with the
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ldisc reference release from the signalled reader/writer, the hangup
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can hang. The new reader/writer is sleeping in ldsem_down_read() and the
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hangup is sleeping in ldsem_down_write() [1].
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The new reader/writer fails to wakeup the waiting hangup because the
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wrong lock count value is checked (the old lock count rather than the new
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lock count) to see if the lock is unowned.
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Change helper function to return the new lock count if the cmpxchg was
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successful; document this behavior.
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[1] edited dmesg log from reporter
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SysRq : Show Blocked State
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task PC stack pid father
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systemd D ffff88040c4f0000 0 1 0 0x00000000
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ffff88040c49fbe0 0000000000000046 ffff88040c4a0000 ffff88040c49ffd8
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00000000001d3980 00000000001d3980 ffff88040c4a0000 ffff88040593d840
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ffff88040c49fb40 ffffffff810a4cc0 0000000000000006 0000000000000023
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Call Trace:
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff817a6649>] schedule+0x24/0x5e
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[<ffffffff817a588b>] schedule_timeout+0x15b/0x1ec
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff817aa691>] ? _raw_spin_unlock_irq+0x24/0x26
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[<ffffffff817aa10c>] down_read_failed+0xe3/0x1b9
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[<ffffffff817aa26d>] ldsem_down_read+0x8b/0xa5
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[<ffffffff8142b5ca>] ? tty_ldisc_ref_wait+0x1b/0x44
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[<ffffffff8142b5ca>] tty_ldisc_ref_wait+0x1b/0x44
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[<ffffffff81423f5b>] tty_write+0x7d/0x28a
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[<ffffffff814241f5>] redirected_tty_write+0x8d/0x98
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[<ffffffff81424168>] ? tty_write+0x28a/0x28a
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[<ffffffff8115d03f>] do_loop_readv_writev+0x56/0x79
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[<ffffffff8115e604>] do_readv_writev+0x1b0/0x1ff
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[<ffffffff8116ea0b>] ? do_vfs_ioctl+0x32a/0x489
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[<ffffffff81167d9d>] ? final_putname+0x1d/0x3a
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[<ffffffff8115e6c7>] vfs_writev+0x2e/0x49
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[<ffffffff8115e7d3>] SyS_writev+0x47/0xaa
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[<ffffffff817ab822>] system_call_fastpath+0x16/0x1b
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bash D ffffffff81c104c0 0 5469 5302 0x00000082
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ffff8800cf817ac0 0000000000000046 ffff8804086b22a0 ffff8800cf817fd8
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00000000001d3980 00000000001d3980 ffff8804086b22a0 ffff8800cf817a48
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000000000000b9a0 ffff8800cf817a78 ffffffff81004675 ffff8800cf817a44
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Call Trace:
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[<ffffffff81004675>] ? dump_trace+0x165/0x29c
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff8100edda>] ? save_stack_trace+0x26/0x41
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[<ffffffff817a6649>] schedule+0x24/0x5e
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[<ffffffff817a588b>] schedule_timeout+0x15b/0x1ec
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[<ffffffff810a4cc0>] ? sched_clock_cpu+0x9f/0xe4
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[<ffffffff817a9f03>] ? down_write_failed+0xa3/0x1c9
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[<ffffffff817aa691>] ? _raw_spin_unlock_irq+0x24/0x26
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[<ffffffff817a9f0b>] down_write_failed+0xab/0x1c9
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[<ffffffff817aa300>] ldsem_down_write+0x79/0xb1
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[<ffffffff817aada3>] ? tty_ldisc_lock_pair_timeout+0xa5/0xd9
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[<ffffffff817aada3>] tty_ldisc_lock_pair_timeout+0xa5/0xd9
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[<ffffffff8142bf33>] tty_ldisc_hangup+0xc4/0x218
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[<ffffffff81423ab3>] __tty_hangup+0x2e2/0x3ed
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[<ffffffff81424a76>] disassociate_ctty+0x63/0x226
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[<ffffffff81078aa7>] do_exit+0x79f/0xa11
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[<ffffffff81086bdb>] ? get_signal_to_deliver+0x206/0x62f
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[<ffffffff810b4bfb>] ? lock_release_holdtime.part.8+0xf/0x16e
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[<ffffffff81079b05>] do_group_exit+0x47/0xb5
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[<ffffffff81086c16>] get_signal_to_deliver+0x241/0x62f
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[<ffffffff810020a7>] do_signal+0x43/0x59d
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[<ffffffff810f2af7>] ? __audit_syscall_exit+0x21a/0x2a8
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[<ffffffff810b4bfb>] ? lock_release_holdtime.part.8+0xf/0x16e
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[<ffffffff81002655>] do_notify_resume+0x54/0x6c
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[<ffffffff817abaf8>] int_signal+0x12/0x17
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Reported-by: Sami Farin <sami.farin@gmail.com>
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Cc: <stable@vger.kernel.org> # 3.12.x
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Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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drivers/tty/tty_ldsem.c | 16 +++++++++++++---
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1 file changed, 13 insertions(+), 3 deletions(-)
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diff --git a/drivers/tty/tty_ldsem.c b/drivers/tty/tty_ldsem.c
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index 22fad8a..d8a55e8 100644
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--- a/drivers/tty/tty_ldsem.c
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+++ b/drivers/tty/tty_ldsem.c
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@@ -86,11 +86,21 @@ static inline long ldsem_atomic_update(long delta, struct ld_semaphore *sem)
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return atomic_long_add_return(delta, (atomic_long_t *)&sem->count);
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}
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+/*
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+ * ldsem_cmpxchg() updates @*old with the last-known sem->count value.
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+ * Returns 1 if count was successfully changed; @*old will have @new value.
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+ * Returns 0 if count was not changed; @*old will have most recent sem->count
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+ */
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static inline int ldsem_cmpxchg(long *old, long new, struct ld_semaphore *sem)
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{
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- long tmp = *old;
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- *old = atomic_long_cmpxchg(&sem->count, *old, new);
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- return *old == tmp;
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+ long tmp = atomic_long_cmpxchg(&sem->count, *old, new);
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+ if (tmp == *old) {
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+ *old = new;
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+ return 1;
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+ } else {
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+ *old = tmp;
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+ return 0;
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+ }
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}
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/*
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--
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cgit v1.1
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