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authorPeter Zijlstra <peterz@infradead.org>2017-10-04 11:13:37 +0200
committerIngo Molnar <mingo@kernel.org>2017-10-10 10:04:28 +0200
commit8b405d5c5d0996d3d16f70c42744a0500f5b6ec3 (patch)
tree3cac3b08d64fc4cda870579eaef748f955ec2c08 /lib
parent529a86e063e9ff625c4ff247d8aa17d8072444fb (diff)
downloadlinux-8b405d5c5d0996d3d16f70c42744a0500f5b6ec3.tar.bz2
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: ce07a9415f26 ("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: ce07a9415f26 ("locking/lockdep: Make check_prev_add() able to handle external stack_trace") Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'lib')
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