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Peter Zijlstra 8b405d5c5d locking/lockdep: Fix stacktrace mess 
There is some complication between check_prevs_add() and
check_prev_add() wrt. saving stack traces. The problem is that we want
to be frugal with saving stack traces, since it consumes static
resources.

We'll only know in check_prev_add() if we need the trace, but we can
call into it multiple times. So we want to do on-demand and re-use.

A further complication is that check_prev_add() can drop graph_lock
and mess with our static resources.

In any case, the current state; after commit:

  ce07a9415f ("locking/lockdep: Make check_prev_add() able to handle external stack_trace")

is that we'll assume the trace contains valid data once
check_prev_add() returns '2'. However, as noted by Josh, this is
false, check_prev_add() can return '2' before having saved a trace,
this then result in the possibility of using uninitialized data.
Testing, as reported by Wu, shows a NULL deref.

So simplify.

Since the graph_lock() thing is a debug path that hasn't
really been used in a long while, take it out back and avoid the
head-ache.

Further initialize the stack_trace to a known 'empty' state; as long
as nr_entries == 0, nothing should deref entries. We can then use the
'entries == NULL' test for a valid trace / on-demand saving.

Analyzed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: ce07a9415f ("locking/lockdep: Make check_prev_add() able to handle external stack_trace")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
 		2017-10-10 10:04:28 +02:00
..
Makefile
…
lockdep.c locking/lockdep: Fix stacktrace mess 2017-10-10 10:04:28 +02:00
lockdep_internals.h locking/lockdep: Avoid creating redundant links 2017-08-10 12:29:04 +02:00
lockdep_proc.c locking/lockdep: Avoid creating redundant links 2017-08-10 12:29:04 +02:00
lockdep_states.h locking/lockdep: Rework FS_RECLAIM annotation 2017-08-10 12:29:03 +02:00
locktorture.c
…
mcs_spinlock.h
…
mutex-debug.c
…
mutex-debug.h
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mutex.c mutex, futex: adjust kernel-doc markups to generate ReST 2017-05-16 08:43:25 -03:00
mutex.h
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osq_lock.c locking/osq_lock: Fix osq_lock queue corruption 2017-08-10 12:28:54 +02:00
percpu-rwsem.c
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qrwlock.c kernel/locking: Fix compile error with qrwlock.c 2017-05-25 12:06:50 -07:00
qspinlock.c locking: Remove spin_unlock_wait() generic definitions 2017-08-17 08:08:58 -07:00
qspinlock_paravirt.h locking/pvqspinlock: Relax cmpxchg's to improve performance on some architectures 2017-08-29 15:14:38 +02:00
qspinlock_stat.h
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rtmutex-debug.c locking/rtmutex: replace top-waiter and pi_waiters leftmost caching 2017-09-08 18:26:49 -07:00
rtmutex-debug.h rt_mutex: Add lockdep annotations 2017-06-08 10:35:49 +02:00
rtmutex.c locking/rtmutex: replace top-waiter and pi_waiters leftmost caching 2017-09-08 18:26:49 -07:00
rtmutex.h rt_mutex: Add lockdep annotations 2017-06-08 10:35:49 +02:00
rtmutex_common.h locking/rtmutex: replace top-waiter and pi_waiters leftmost caching 2017-09-08 18:26:49 -07:00
rwsem-spinlock.c locking/rwsem-spinlock: Add killable versions of __down_read() 2017-08-10 12:28:55 +02:00
rwsem-xadd.c locking/rwsem-xadd: Fix missed wakeup due to reordering of load 2017-09-29 10:10:20 +02:00
rwsem.c
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rwsem.h
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semaphore.c
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spinlock.c
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spinlock_debug.c
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test-ww_mutex.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00