Commit a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer
in use") changed the behavior of lockdep_free_key_range() from
unconditionally zapping lock classes into only zapping lock classes if
debug_lock == true. Not zapping lock classes if debug_lock == false leaves
dangling pointers in several lockdep datastructures, e.g. lock_class::name
in the all_lock_classes list. The shell command "cat /proc/lockdep" causes
the kernel to iterate the all_lock_classes list. Hence the "unable to
handle kernel paging request" issue that Shenghui encountered by running
cat /proc/lockdep. Since the new behavior can cause cat /proc/lockdep to
crash, restore the pre-v5.1 behavior.
This patch avoids that cat /proc/lockdep triggers the following crash
with debug_lock == false:
BUG: unable to handle kernel paging request at fffffbfff40ca448
PGD 13bfde067 P4D 13bfde067 PUD 13bf7a067 PMD 1167d3067 PTE 0
Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 4 PID: 4529 Comm: cat Tainted: G B W O 5.1.0-rc1-dbg+ #4
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
RIP: 0010:__asan_load1+0x28/0x50
Call Trace:
string+0xac/0x180
vsnprintf+0x23e/0x820
seq_vprintf+0x82/0xc0
seq_printf+0x92/0xb0
print_name+0x34/0xb0
l_show+0x184/0x200
seq_read+0x59e/0x6c0
proc_reg_read+0x11f/0x170
__vfs_read+0x4d/0x90
vfs_read+0xc5/0x1f0
ksys_read+0xab/0x130
__x64_sys_read+0x43/0x50
do_syscall_64+0x71/0x210
entry_SYSCALL_64_after_hwframe+0x49/0xbe
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Waiman Long <long...@redhat.com>
Cc: shenghui <shh...@foxmail.com>
Reported-by: shenghui <shh...@foxmail.com>
Fixes: a0b0fd53e1e6 ("locking/lockdep: Free lock classes that are no longer in
use") # v5.1-rc1.
Signed-off-by: Bart Van Assche <bvanass...@acm.org>
---
Changes compared to v1:
- Restored lockdep recursion protection.
- Made patch description more detailed.
kernel/locking/lockdep.c | 29 ++++++++++++-----------------
1 file changed, 12 insertions(+), 17 deletions(-)
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 34cdcbedda49..e16766ff184b 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4689,8 +4689,8 @@ static void free_zapped_rcu(struct rcu_head *ch)
return;
raw_local_irq_save(flags);
- if (!graph_lock())
- goto out_irq;
+ arch_spin_lock(&lockdep_lock);
+ current->lockdep_recursion = 1;
/* closed head */
pf = delayed_free.pf + (delayed_free.index ^ 1);
@@ -4702,8 +4702,8 @@ static void free_zapped_rcu(struct rcu_head *ch)
*/
call_rcu_zapped(delayed_free.pf + delayed_free.index);
- graph_unlock();
-out_irq:
+ current->lockdep_recursion = 0;
+ arch_spin_unlock(&lockdep_lock);
raw_local_irq_restore(flags);
}
@@ -4744,21 +4744,17 @@ static void lockdep_free_key_range_reg(void *start,
unsigned long size)
{
struct pending_free *pf;
unsigned long flags;
- int locked;
init_data_structures_once();
raw_local_irq_save(flags);
- locked = graph_lock();
- if (!locked)
- goto out_irq;
-
+ arch_spin_lock(&lockdep_lock);
+ current->lockdep_recursion = 1;
pf = get_pending_free();
__lockdep_free_key_range(pf, start, size);
call_rcu_zapped(pf);
-
- graph_unlock();
-out_irq:
+ current->lockdep_recursion = 0;
+ arch_spin_unlock(&lockdep_lock);
raw_local_irq_restore(flags);
/*
@@ -4911,9 +4907,8 @@ void lockdep_unregister_key(struct lock_class_key *key)
return;
raw_local_irq_save(flags);
- if (!graph_lock())
- goto out_irq;
-
+ arch_spin_lock(&lockdep_lock);
+ current->lockdep_recursion = 1;
pf = get_pending_free();
hlist_for_each_entry_rcu(k, hash_head, hash_entry) {
if (k == key) {
@@ -4925,8 +4920,8 @@ void lockdep_unregister_key(struct lock_class_key *key)
WARN_ON_ONCE(!found);
__lockdep_free_key_range(pf, key, 1);
call_rcu_zapped(pf);
- graph_unlock();
-out_irq:
+ current->lockdep_recursion = 0;
+ arch_spin_unlock(&lockdep_lock);
raw_local_irq_restore(flags);
/* Wait until is_dynamic_key() has finished accessing k->hash_entry. */
--
2.21.0.196.g041f5ea1cf98
