Messages in this thread Patch in this message | | | Date | Wed, 30 Sep 2020 11:49:37 +0200 | From | Peter Zijlstra <> | Subject | Re: lockdep null-ptr-deref |
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On Wed, Sep 30, 2020 at 11:16:11AM +0200, Peter Zijlstra wrote: > On Wed, Sep 30, 2020 at 07:08:23AM +0800, Boqun Feng wrote: > > I think there are two problems here: > > > > 1) the "(null)" means we don't have the "usage_str" for a usage bit, > > which I think is the LOCK_USED_READ bit introduced by Peter at > > 23870f122768 ('locking/lockdep: Fix "USED" <- "IN-NMI" inversions'). > > > > 2) the next null-ptr-deref, and I think this is also caused by > > LOCK_USED_READ bit, because in the loop inside > > print_lock_class_header(), we iterate from 0 to LOCK_USAGE_STATES (which > > is 4*2 + 3), however the class->usage_traces[] only has > > XXX_LOCK_USAGE_STATES (which is 4*2 + 1) elements, so if we have > > LOCK_USED_READ bit set in ->usage_mask, we will try to access an element > > out of the ->usage_traces[] array. > > > > Probably the following helps? And another possible fix is to enlarge the > > ->usage_trace[] array and record the call trace of LOCK_READ_USED. > > Urgh.. yeah, I wanted to avoid saving that trace; it's pretty useless :/ > The existing USED trace is already mostly pointless, the consistent > thing would be to remove both but that might be too radical. > > But you're right in that I made a right mess of it. Not sure what's > best here. > > Let me have a play.
How's something like this? It's bigger than I'd like, but I feel the result is more consistent/readable.
--- diff --git a/include/linux/lockdep_types.h b/include/linux/lockdep_types.h index bb35b449f533..a55b1d314ae8 100644 --- a/include/linux/lockdep_types.h +++ b/include/linux/lockdep_types.h @@ -35,8 +35,12 @@ enum lockdep_wait_type { /* * We'd rather not expose kernel/lockdep_states.h this wide, but we do need * the total number of states... :-( + * + * XXX_LOCK_USAGE_STATES is the number of lines in lockdep_states.h, for each + * of those we generates 4 states, Additionally we (for now) report on USED. */ -#define XXX_LOCK_USAGE_STATES (1+2*4) +#define XXX_LOCK_USAGE_STATES 2 +#define LOCK_TRACE_STATES (XXX_LOCK_USAGE_STATES*4 + 1) /* * NR_LOCKDEP_CACHING_CLASSES ... Number of classes @@ -106,7 +110,7 @@ struct lock_class { * IRQ/softirq usage tracking bits: */ unsigned long usage_mask; - const struct lock_trace *usage_traces[XXX_LOCK_USAGE_STATES]; + const struct lock_trace *usage_traces[LOCK_TRACE_STATES]; /* * Generation counter, when doing certain classes of graph walking, diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index 454355c033d2..4f98ac8b4575 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -600,6 +600,8 @@ static const char *usage_str[] = #include "lockdep_states.h" #undef LOCKDEP_STATE [LOCK_USED] = "INITIAL USE", + [LOCK_USED_READ] = "INITIAL READ USE", + /* abused as string storage for verify_lock_unused() */ [LOCK_USAGE_STATES] = "IN-NMI", }; #endif @@ -2231,7 +2233,7 @@ static void print_lock_class_header(struct lock_class *class, int depth) #endif printk(KERN_CONT " {\n"); - for (bit = 0; bit < LOCK_USAGE_STATES; bit++) { + for (bit = 0; bit < LOCK_TRACE_STATES; bit++) { if (class->usage_mask & (1 << bit)) { int len = depth; @@ -4354,27 +4356,24 @@ static int mark_lock(struct task_struct *curr, struct held_lock *this, old_mask = hlock_class(this)->usage_mask; hlock_class(this)->usage_mask |= new_mask; - /* - * Save one usage_traces[] entry and map both LOCK_USED and - * LOCK_USED_READ onto the same entry. - */ - if (new_bit == LOCK_USED || new_bit == LOCK_USED_READ) { - if (old_mask & (LOCKF_USED | LOCKF_USED_READ)) - goto unlock; - new_bit = LOCK_USED; + if (new_bit < LOCK_TRACE_STATES) { + if (!(hlock_class(this)->usage_traces[new_bit] = save_trace())) + return 0; } - if (!(hlock_class(this)->usage_traces[new_bit] = save_trace())) - return 0; - switch (new_bit) { + case 0 ... LOCK_USED-1: + ret = mark_lock_irq(curr, this, new_bit); + if (!ret) + return 0; + break; + case LOCK_USED: debug_atomic_dec(nr_unused_locks); break; + default: - ret = mark_lock_irq(curr, this, new_bit); - if (!ret) - return 0; + break; } unlock: diff --git a/kernel/locking/lockdep_internals.h b/kernel/locking/lockdep_internals.h index b0be1560ed17..67dc46e46552 100644 --- a/kernel/locking/lockdep_internals.h +++ b/kernel/locking/lockdep_internals.h @@ -20,9 +20,12 @@ enum lock_usage_bit { #undef LOCKDEP_STATE LOCK_USED, LOCK_USED_READ, - LOCK_USAGE_STATES + LOCK_USAGE_STATES, }; +/* states after LOCK_USED are not traced and printed */ +static_assert(LOCK_TRACE_STATES == LOCK_USED_READ); + #define LOCK_USAGE_READ_MASK 1 #define LOCK_USAGE_DIR_MASK 2 #define LOCK_USAGE_STATE_MASK (~(LOCK_USAGE_READ_MASK | LOCK_USAGE_DIR_MASK)) @@ -121,7 +124,7 @@ static const unsigned long LOCKF_USED_IN_IRQ_READ = extern struct list_head all_lock_classes; extern struct lock_chain lock_chains[]; -#define LOCK_USAGE_CHARS (1+LOCK_USAGE_STATES/2) +#define LOCK_USAGE_CHARS (2*XXX_LOCK_USAGE_STATES + 1) extern void get_usage_chars(struct lock_class *class, char usage[LOCK_USAGE_CHARS]);
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