On Wed, Mar 18, 2026 at 02:30:37PM +0900, Yunseong Kim wrote: > Hi Tzung-Bi, > > Thanks for the great work! > > I'm very interested in this work as it will be helpful for verifying > whether kernel crash dumps are correctly extracted when a deadlock is > detected by lockdep. I really hope to see this merged. > > I have a couple of questions regarding the organization of these tests: > > Is the intent of this new lockdep.c specifically to validate the lockdep > infrastructure itself rather than providing general deadlock.c code It > feels like "deadlock" might be a broader category. For example, DEPT > (Dependency Tracker) can track wait/event dependencies for > PG_locked/writeback. > I'm planning a follow-up contribution to cover these cases that DEPT can > detect.
Yes, the lockdep.c is designed for lockdep; "deadlock" should be a different set of issues (e.g., lockdep isn't only for deadlock). > > Do you think it would be better to implement deadlock detection for LKDTM > (like the ones DEPT handles) in a separate deadlock.c instead of > lockdep.c? I'd love to hear your thoughts on the scope. I think separate them would be easier to understand and review. > > Best regards, > Yunseong > > On 12/15/25 4:25 PM, Tzung-Bi Shih wrote: > > Introduce various lockdep related crash tests. > > > > Signed-off-by: Tzung-Bi Shih <[email protected]> > > --- > > v3: > > - Add some entries in tools/testing/selftests/lkdtm/tests.txt. > > > > v2: https://lore.kernel.org/all/[email protected]/ > > - Fix "warning: suggest braces around empty body in an 'else' statement > > [-Wempty-body]" > > reported by 0day test robot. > > > > v1: > > https://lore.kernel.org/lkml/[email protected]/T/#u > > > > drivers/misc/lkdtm/Makefile | 1 + > > drivers/misc/lkdtm/core.c | 1 + > > drivers/misc/lkdtm/lkdtm.h | 1 + > > drivers/misc/lkdtm/lockdep.c | 98 +++++++++++++++++++++++++ > > tools/testing/selftests/lkdtm/tests.txt | 8 ++ > > 5 files changed, 109 insertions(+) > > create mode 100644 drivers/misc/lkdtm/lockdep.c > > > > diff --git a/drivers/misc/lkdtm/Makefile b/drivers/misc/lkdtm/Makefile > > index 03ebe33185f9..830b71c8e6a0 100644 > > --- a/drivers/misc/lkdtm/Makefile > > +++ b/drivers/misc/lkdtm/Makefile > > @@ -11,6 +11,7 @@ lkdtm-$(CONFIG_LKDTM) += usercopy.o > > lkdtm-$(CONFIG_LKDTM) += kstack_erase.o > > lkdtm-$(CONFIG_LKDTM) += cfi.o > > lkdtm-$(CONFIG_LKDTM) += fortify.o > > +lkdtm-$(CONFIG_LKDTM) += lockdep.o > > lkdtm-$(CONFIG_PPC_64S_HASH_MMU) += powerpc.o > > > > KASAN_SANITIZE_stackleak.o := n > > diff --git a/drivers/misc/lkdtm/core.c b/drivers/misc/lkdtm/core.c > > index 5732fd59a227..43e91388940f 100644 > > --- a/drivers/misc/lkdtm/core.c > > +++ b/drivers/misc/lkdtm/core.c > > @@ -96,6 +96,7 @@ static const struct crashtype_category > > *crashtype_categories[] = { > > &stackleak_crashtypes, > > &cfi_crashtypes, > > &fortify_crashtypes, > > + &lockdep_crashtypes, > > #ifdef CONFIG_PPC_64S_HASH_MMU > > &powerpc_crashtypes, > > #endif > > diff --git a/drivers/misc/lkdtm/lkdtm.h b/drivers/misc/lkdtm/lkdtm.h > > index 015e0484026b..d2d97e6f323e 100644 > > --- a/drivers/misc/lkdtm/lkdtm.h > > +++ b/drivers/misc/lkdtm/lkdtm.h > > @@ -84,6 +84,7 @@ extern struct crashtype_category usercopy_crashtypes; > > extern struct crashtype_category stackleak_crashtypes; > > extern struct crashtype_category cfi_crashtypes; > > extern struct crashtype_category fortify_crashtypes; > > +extern struct crashtype_category lockdep_crashtypes; > > extern struct crashtype_category powerpc_crashtypes; > > > > /* Each category's init/exit routines. */ > > diff --git a/drivers/misc/lkdtm/lockdep.c b/drivers/misc/lkdtm/lockdep.c > > new file mode 100644 > > index 000000000000..e029e9e60ce6 > > --- /dev/null > > +++ b/drivers/misc/lkdtm/lockdep.c > > @@ -0,0 +1,98 @@ > > +// SPDX-License-Identifier: GPL-2.0 > > +/* > > + * Copyright 2025 Google LLC > > + * > > + * Tests related to lockdep warnings. > > + */ > > +#include "lkdtm.h" > > +#include <linux/cleanup.h> > > +#include <linux/irqflags.h> > > +#include <linux/mutex.h> > > +#include <linux/spinlock.h> > > +#include <linux/srcu.h> > > + > > +static DEFINE_SPINLOCK(lock_A); > > +static DEFINE_SPINLOCK(lock_B); > > + > > +/* For "WARNING: possible circular locking dependency detected". */ > > +static void lkdtm_LOCKDEP_CIRCULAR_LOCK(void) > > +{ > > + scoped_guard(spinlock, &lock_A) > > + scoped_guard(spinlock, &lock_B) {} > > + scoped_guard(spinlock, &lock_B) > > + scoped_guard(spinlock, &lock_A) {} > > +} > > + > > +/* For "WARNING: possible recursive locking detected". */ > > +static void lkdtm_LOCKDEP_RECURSIVE_LOCK(void) > > +{ > > + guard(spinlock)(&lock_A); > > + guard(spinlock)(&lock_A); > > +} > > + > > +/* For "WARNING: inconsistent lock state". */ > > +static void lkdtm_LOCKDEP_INCONSISTENT_LOCK(void) > > +{ > > + lockdep_softirq_enter(); > > + scoped_guard(spinlock, &lock_A) {} > > + lockdep_softirq_exit(); > > + > > + scoped_guard(spinlock, &lock_A) {} > > +} > > + > > +/* For "WARNING: Nested lock was not taken". */ > > +static void lkdtm_LOCKDEP_NESTED_LOCK_NOT_HELD(void) > > +{ > > + spin_lock_nest_lock(&lock_B, &lock_A); > > +} > > + > > +/* For "WARNING: bad unlock balance detected!". */ > > +static void lkdtm_LOCKDEP_BAD_UNLOCK_BALANCE(void) > > +{ > > + spin_unlock(&lock_A); > > +} > > + > > +/* For "WARNING: held lock freed!". */ > > +static void lkdtm_LOCKDEP_HELD_LOCK_FREED(void) > > +{ > > + spin_lock(&lock_A); > > + spin_lock_init(&lock_A); > > +} > > + > > +/* For "WARNING: lock held when returning to user space!". */ > > +static void lkdtm_LOCKDEP_HELD_LOCK(void) > > +{ > > + spin_lock(&lock_A); > > +} > > + > > +/* For "WARNING: suspicious RCU usage". */ > > +static void lkdtm_LOCKDEP_SUSPICIOUS_RCU(void) > > +{ > > + struct srcu_struct srcu; > > + void __rcu *res = NULL; > > + int idx; > > + > > + init_srcu_struct(&srcu); > > + > > + idx = srcu_read_lock(&srcu); > > + rcu_dereference(res); > > + srcu_read_unlock(&srcu, idx); > > + > > + cleanup_srcu_struct(&srcu); > > +} > > + > > +static struct crashtype crashtypes[] = { > > + CRASHTYPE(LOCKDEP_CIRCULAR_LOCK), > > + CRASHTYPE(LOCKDEP_RECURSIVE_LOCK), > > + CRASHTYPE(LOCKDEP_INCONSISTENT_LOCK), > > + CRASHTYPE(LOCKDEP_NESTED_LOCK_NOT_HELD), > > + CRASHTYPE(LOCKDEP_BAD_UNLOCK_BALANCE), > > + CRASHTYPE(LOCKDEP_HELD_LOCK_FREED), > > + CRASHTYPE(LOCKDEP_HELD_LOCK), > > + CRASHTYPE(LOCKDEP_SUSPICIOUS_RCU), > > +}; > > + > > +struct crashtype_category lockdep_crashtypes = { > > + .crashtypes = crashtypes, > > + .len = ARRAY_SIZE(crashtypes), > > +}; > > diff --git a/tools/testing/selftests/lkdtm/tests.txt > > b/tools/testing/selftests/lkdtm/tests.txt > > index cff124c1eddd..7b32dece3d3a 100644 > > --- a/tools/testing/selftests/lkdtm/tests.txt > > +++ b/tools/testing/selftests/lkdtm/tests.txt > > @@ -83,3 +83,11 @@ FORTIFY_STR_MEMBER detected buffer overflow > > FORTIFY_MEM_OBJECT detected buffer overflow > > FORTIFY_MEM_MEMBER detected field-spanning write > > PPC_SLB_MULTIHIT Recovered > > +#LOCKDEP_CIRCULAR_LOCK Lockdep can only trigger once > > +#LOCKDEP_RECURSIVE_LOCK Hangs the system > > +#LOCKDEP_INCONSISTENT_LOCK Lockdep can only trigger once > > +#LOCKDEP_NESTED_LOCK_NOT_HELD Cause a deadlock in subsequent lockdep tests > > +#LOCKDEP_BAD_UNLOCK_BALANCE Lockdep can only trigger once > > +#LOCKDEP_HELD_LOCK_FREED Lockdep can only trigger once > > +#LOCKDEP_HELD_LOCK Cause a deadlock in subsequent lockdep tests > > +#LOCKDEP_SUSPICIOUS_RCU Lockdep can only trigger once >
