Messages in this thread Patch in this message | | | From | Frederic Weisbecker <> | Subject | [PATCH 04/32] locking/lockdep: Test all incompatible scenario at once in check_irq_usage() | Date | Tue, 12 Feb 2019 18:13:55 +0100 |
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check_prev_add_irq() tests all incompatible scenarios one after the other while adding a lock (@next) to a tree dependency (@prev):
LOCK_USED_IN_HARDIRQ vs LOCK_ENABLED_HARDIRQ LOCK_USED_IN_HARDIRQ_READ vs LOCK_ENABLED_HARDIRQ LOCK_USED_IN_SOFTIRQ vs LOCK_ENABLED_SOFTIRQ LOCK_USED_IN_SOFTIRQ_READ vs LOCK_ENABLED_SOFTIRQ
Also for these four scenarios, we must at least iterate the @prev backward dependency. Then if it matches the relevant LOCK_USED_* bit, we must also iterate the @next forward dependency.
Therefore in the best case we iterate 4 times, in the worst case 8 times.
Now things are going to become much worse as we plan to add as much LOCK_USED_IN_{$VEC}_SOFTIRQ[_READ] as we have softirq vectors, currently 10. So the expanded test would be at least 22 loops and at most 44. We can't really afford that.
So we take a different approach to fix this:
1) Iterate through @prev backward dependencies and accumulate all the IRQ uses in a single mask.
2) Iterate through @next forward dependencies and try to find a lock whose usage is exclusive to the accumulated usages gathered in the previous step. If we find one (call it @lockA), we have found an incompatible use.
3) Iterate again through @prev backward dependency and find the lock whose usage matches @lockA in term of incompatibility. Call that lock @lockB.
4) Report the incompatible usages of @lockA and @lockB
If no incompatible use is found, the verification never goes beyond step 2 which means at most two iterations.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Pavan Kondeti <pkondeti@codeaurora.org> Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com> Cc: David S . Miller <davem@davemloft.net> Cc: Ingo Molnar <mingo@kernel.org> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> --- kernel/locking/lockdep.c | 204 ++++++++++++++++++++++++++------------- 1 file changed, 137 insertions(+), 67 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c index a977aa5976b7..578dd57f70d3 100644 --- a/kernel/locking/lockdep.c +++ b/kernel/locking/lockdep.c @@ -1329,6 +1329,14 @@ check_redundant(struct lock_list *root, struct lock_class *target, } #if defined(CONFIG_TRACE_IRQFLAGS) && defined(CONFIG_PROVE_LOCKING) + +static inline int usage_accumulate(struct lock_list *entry, void *mask) +{ + *(u64 *)mask |= entry->class->usage_mask; + + return 0; +} + /* * Forwards and backwards subgraph searching, for the purposes of * proving that two subgraphs can be connected by a new dependency @@ -1340,8 +1348,6 @@ static inline int usage_match(struct lock_list *entry, void *mask) return entry->class->usage_mask & *(u64 *)mask; } - - /* * Find a node in the forwards-direction dependency sub-graph starting * at @root->class that matches @bit. @@ -1575,39 +1581,6 @@ print_bad_irq_dependency(struct task_struct *curr, return 0; } -static int -check_usage(struct task_struct *curr, struct held_lock *prev, - struct held_lock *next, enum lock_usage_bit bit_backwards, - enum lock_usage_bit bit_forwards, const char *irqclass) -{ - int ret; - struct lock_list this, that; - struct lock_list *uninitialized_var(target_entry); - struct lock_list *uninitialized_var(target_entry1); - - this.parent = NULL; - - this.class = hlock_class(prev); - ret = find_usage_backwards(&this, BIT(bit_backwards), &target_entry); - if (ret < 0) - return print_bfs_bug(ret); - if (ret == 1) - return ret; - - that.parent = NULL; - that.class = hlock_class(next); - ret = find_usage_forwards(&that, BIT(bit_forwards), &target_entry1); - if (ret < 0) - return print_bfs_bug(ret); - if (ret == 1) - return ret; - - return print_bad_irq_dependency(curr, &this, &that, - target_entry, target_entry1, - prev, next, - bit_backwards, bit_forwards, irqclass); -} - static const char *state_names[] = { #define LOCKDEP_STATE(__STATE) \ __stringify(__STATE), @@ -1638,45 +1611,143 @@ static int exclusive_bit(int new_bit) return state | (dir ^ LOCK_USAGE_DIR_MASK); } +static u64 __invert_mask(u64 mask, bool read) +{ + u64 excl_mask = 0; + int bit = 0; + + while (mask) { + long fs = __ffs64(mask) + 1; + int excl; + + mask >>= fs; + bit += fs; + excl = exclusive_bit(bit - 1); + excl_mask |= lock_flag(excl); + if (read) + excl_mask |= lock_flag(excl | LOCK_USAGE_READ_MASK); + } + + return excl_mask; +} + +static u64 exclusive_mask(u64 mask) +{ + return __invert_mask(mask, false); +} + +/* + * Retrieve the _possible_ original mask to which @mask is + * exclusive. Ie: this is the opposite of exclusive_mask(). + * Note that 2 possible original bits can match an exclusive + * bit: one has LOCK_USAGE_READ_MASK set, the other has it + * cleared. So both are returned for each exclusive bit. + */ +static u64 original_mask(u64 mask) +{ + return __invert_mask(mask, true); +} + +/* + * Find the first pair of bit match between an original + * usage mask and an exclusive usage mask. + */ +static int find_exclusive_match(u64 mask, u64 excl_mask, + enum lock_usage_bit *bit, + enum lock_usage_bit *excl_bit) +{ + int nr = 0; + + while (mask) { + long fs = __ffs64(mask) + 1; + int excl; + + mask >>= fs; + nr += fs; + + excl = exclusive_bit(nr - 1); + if (excl_mask & lock_flag(excl)) { + *bit = nr - 1; + *excl_bit = excl; + return 0; + } + } + return -1; +} + +/* + * Prove that the new dependency does not connect a hardirq-safe(-read) + * lock with a hardirq-unsafe lock - to achieve this we search + * the backwards-subgraph starting at <prev>, and the + * forwards-subgraph starting at <next>: + */ static int check_irq_usage(struct task_struct *curr, struct held_lock *prev, - struct held_lock *next, enum lock_usage_bit bit) + struct held_lock *next) { + enum lock_usage_bit forward_bit = 0, backward_bit = 0; + struct lock_list *uninitialized_var(target_entry1); + struct lock_list *uninitialized_var(target_entry); + u64 usage_mask = 0, forward_mask, backward_mask; + struct lock_list this, that; + int ret; + /* - * Prove that the new dependency does not connect a hardirq-safe - * lock with a hardirq-unsafe lock - to achieve this we search - * the backwards-subgraph starting at <prev>, and the - * forwards-subgraph starting at <next>: + * Step 1: gather all hard/soft IRQs usages backward in an + * accumulated usage mask. */ - if (!check_usage(curr, prev, next, bit, - exclusive_bit(bit), state_name(bit))) - return 0; + this.parent = NULL; + this.class = hlock_class(prev); + + ret = __bfs_backwards(&this, &usage_mask, usage_accumulate, NULL); + if (ret < 0) + return print_bfs_bug(ret); - bit++; /* _READ */ + usage_mask &= LOCKF_USED_IN_IRQ | LOCKF_USED_IN_IRQ_READ; + if (!usage_mask) + return 1; /* - * Prove that the new dependency does not connect a hardirq-safe-read - * lock with a hardirq-unsafe lock - to achieve this we search - * the backwards-subgraph starting at <prev>, and the - * forwards-subgraph starting at <next>: + * Step 2: find exclusive uses forward that match the previous + * backward accumulated mask. */ - if (!check_usage(curr, prev, next, bit, - exclusive_bit(bit), state_name(bit))) - return 0; + forward_mask = exclusive_mask(usage_mask); - return 1; -} + that.parent = NULL; + that.class = hlock_class(next); -static int -check_prev_add_irq(struct task_struct *curr, struct held_lock *prev, - struct held_lock *next) -{ -#define LOCKDEP_STATE(__STATE) \ - if (!check_irq_usage(curr, prev, next, LOCK_USED_IN_##__STATE)) \ - return 0; -#include "lockdep_states.h" -#undef LOCKDEP_STATE + ret = find_usage_forwards(&that, forward_mask, &target_entry1); + if (ret < 0) + return print_bfs_bug(ret); + if (ret == 1) + return ret; + + /* + * Step 3: we found a bad match! Now retrieve a lock from the backward + * list whose usage mask matches the exclusive usage mask from the + * lock found on the forward list. + */ + backward_mask = original_mask(target_entry1->class->usage_mask); + + ret = find_usage_backwards(&this, backward_mask, &target_entry); + if (ret < 0) + return print_bfs_bug(ret); + if (ret == 1) + return print_bfs_bug(ret); + + /* + * Step 4: narrow down to a pair of incompatible usage bits + * and report it. + */ + ret = find_exclusive_match(target_entry->class->usage_mask, + target_entry1->class->usage_mask, + &backward_bit, &forward_bit); + WARN_ON_ONCE(ret == -1); - return 1; + return print_bad_irq_dependency(curr, &this, &that, + target_entry, target_entry1, + prev, next, + backward_bit, forward_bit, + state_name(backward_bit)); } static void inc_chains(void) @@ -1693,9 +1764,8 @@ static void inc_chains(void) #else -static inline int -check_prev_add_irq(struct task_struct *curr, struct held_lock *prev, - struct held_lock *next) +static inline int check_irq_usage(struct task_struct *curr, + struct held_lock *prev, struct held_lock *next) { return 1; } @@ -1857,7 +1927,7 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, else if (unlikely(ret < 0)) return print_bfs_bug(ret); - if (!check_prev_add_irq(curr, prev, next)) + if (!check_irq_usage(curr, prev, next)) return 0; /* -- 2.17.1
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