Commit 1a365e82 authored by Marco Elver's avatar Marco Elver Committed by Ingo Molnar
Browse files

locking/spinlock/debug: Fix various data races 



This fixes various data races in spinlock_debug. By testing with KCSAN,
it is observable that the console gets spammed with data races reports,
suggesting these are extremely frequent.

Example data race report:

  read to 0xffff8ab24f403c48 of 4 bytes by task 221 on cpu 2:
   debug_spin_lock_before kernel/locking/spinlock_debug.c:85 [inline]
   do_raw_spin_lock+0x9b/0x210 kernel/locking/spinlock_debug.c:112
   __raw_spin_lock include/linux/spinlock_api_smp.h:143 [inline]
   _raw_spin_lock+0x39/0x40 kernel/locking/spinlock.c:151
   spin_lock include/linux/spinlock.h:338 [inline]
   get_partial_node.isra.0.part.0+0x32/0x2f0 mm/slub.c:1873
   get_partial_node mm/slub.c:1870 [inline]
  <snip>

  write to 0xffff8ab24f403c48 of 4 bytes by task 167 on cpu 3:
   debug_spin_unlock kernel/locking/spinlock_debug.c:103 [inline]
   do_raw_spin_unlock+0xc9/0x1a0 kernel/locking/spinlock_debug.c:138
   __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:159 [inline]
   _raw_spin_unlock_irqrestore+0x2d/0x50 kernel/locking/spinlock.c:191
   spin_unlock_irqrestore include/linux/spinlock.h:393 [inline]
   free_debug_processing+0x1b3/0x210 mm/slub.c:1214
   __slab_free+0x292/0x400 mm/slub.c:2864
  <snip>

As a side-effect, with KCSAN, this eventually locks up the console, most
likely due to deadlock, e.g. .. -> printk lock -> spinlock_debug ->
KCSAN detects data race -> kcsan_print_report() -> printk lock ->
deadlock.

This fix will 1) avoid the data races, and 2) allow using lock debugging
together with KCSAN.

Reported-by: default avatarQian Cai <cai@lca.pw>
Signed-off-by: default avatarMarco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will.deacon@arm.com>
Link: https://lkml.kernel.org/r/20191120155715.28089-1-elver@google.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent c2da5bdc

kernel/locking/spinlock_debug.c

+16 −16
Original line number Diff line number Diff line
@@ -51,19 +51,19 @@ EXPORT_SYMBOL(__rwlock_init); 


static void spin_dump(raw_spinlock_t *lock, const char *msg)

{

	struct task_struct *owner = NULL;

	struct task_struct *owner = READ_ONCE(lock->owner);



	if (lock->owner && lock->owner != SPINLOCK_OWNER_INIT)

		owner = lock->owner;

	if (owner == SPINLOCK_OWNER_INIT)

		owner = NULL;

	printk(KERN_EMERG "BUG: spinlock %s on CPU#%d, %s/%d\n",

		msg, raw_smp_processor_id(),

		current->comm, task_pid_nr(current));

	printk(KERN_EMERG " lock: %pS, .magic: %08x, .owner: %s/%d, "

			".owner_cpu: %d\n",

		lock, lock->magic,

		lock, READ_ONCE(lock->magic),

		owner ? owner->comm : "<none>",

		owner ? task_pid_nr(owner) : -1,

		lock->owner_cpu);

		READ_ONCE(lock->owner_cpu));

	dump_stack();

}
@@ -80,16 +80,16 @@ static void spin_bug(raw_spinlock_t *lock, const char *msg) 
static inline void

debug_spin_lock_before(raw_spinlock_t *lock)

{

	SPIN_BUG_ON(lock->magic != SPINLOCK_MAGIC, lock, "bad magic");

	SPIN_BUG_ON(lock->owner == current, lock, "recursion");

	SPIN_BUG_ON(lock->owner_cpu == raw_smp_processor_id(),

	SPIN_BUG_ON(READ_ONCE(lock->magic) != SPINLOCK_MAGIC, lock, "bad magic");

	SPIN_BUG_ON(READ_ONCE(lock->owner) == current, lock, "recursion");

	SPIN_BUG_ON(READ_ONCE(lock->owner_cpu) == raw_smp_processor_id(),

							lock, "cpu recursion");

}



static inline void debug_spin_lock_after(raw_spinlock_t *lock)

{

	lock->owner_cpu = raw_smp_processor_id();

	lock->owner = current;

	WRITE_ONCE(lock->owner_cpu, raw_smp_processor_id());

	WRITE_ONCE(lock->owner, current);

}



static inline void debug_spin_unlock(raw_spinlock_t *lock)
@@ -99,8 +99,8 @@ static inline void debug_spin_unlock(raw_spinlock_t *lock) 
	SPIN_BUG_ON(lock->owner != current, lock, "wrong owner");

	SPIN_BUG_ON(lock->owner_cpu != raw_smp_processor_id(),

							lock, "wrong CPU");

	lock->owner = SPINLOCK_OWNER_INIT;

	lock->owner_cpu = -1;

	WRITE_ONCE(lock->owner, SPINLOCK_OWNER_INIT);

	WRITE_ONCE(lock->owner_cpu, -1);

}



/*
@@ -187,8 +187,8 @@ static inline void debug_write_lock_before(rwlock_t *lock) 


static inline void debug_write_lock_after(rwlock_t *lock)

{

	lock->owner_cpu = raw_smp_processor_id();

	lock->owner = current;

	WRITE_ONCE(lock->owner_cpu, raw_smp_processor_id());

	WRITE_ONCE(lock->owner, current);

}



static inline void debug_write_unlock(rwlock_t *lock)
@@ -197,8 +197,8 @@ static inline void debug_write_unlock(rwlock_t *lock) 
	RWLOCK_BUG_ON(lock->owner != current, lock, "wrong owner");

	RWLOCK_BUG_ON(lock->owner_cpu != raw_smp_processor_id(),

							lock, "wrong CPU");

	lock->owner = SPINLOCK_OWNER_INIT;

	lock->owner_cpu = -1;

	WRITE_ONCE(lock->owner, SPINLOCK_OWNER_INIT);

	WRITE_ONCE(lock->owner_cpu, -1);

}



void do_raw_write_lock(rwlock_t *lock)

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