linux-stable/kernel/locking
Jason A. Donenfeld 81895a65ec treewide: use prandom_u32_max() when possible, part 1
Rather than incurring a division or requesting too many random bytes for
the given range, use the prandom_u32_max() function, which only takes
the minimum required bytes from the RNG and avoids divisions. This was
done mechanically with this coccinelle script:

@basic@
expression E;
type T;
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
typedef u64;
@@
(
- ((T)get_random_u32() % (E))
+ prandom_u32_max(E)
|
- ((T)get_random_u32() & ((E) - 1))
+ prandom_u32_max(E * XXX_MAKE_SURE_E_IS_POW2)
|
- ((u64)(E) * get_random_u32() >> 32)
+ prandom_u32_max(E)
|
- ((T)get_random_u32() & ~PAGE_MASK)
+ prandom_u32_max(PAGE_SIZE)
)

@multi_line@
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
identifier RAND;
expression E;
@@

-       RAND = get_random_u32();
        ... when != RAND
-       RAND %= (E);
+       RAND = prandom_u32_max(E);

// Find a potential literal
@literal_mask@
expression LITERAL;
type T;
identifier get_random_u32 =~ "get_random_int|prandom_u32|get_random_u32";
position p;
@@

        ((T)get_random_u32()@p & (LITERAL))

// Add one to the literal.
@script:python add_one@
literal << literal_mask.LITERAL;
RESULT;
@@

value = None
if literal.startswith('0x'):
        value = int(literal, 16)
elif literal[0] in '123456789':
        value = int(literal, 10)
if value is None:
        print("I don't know how to handle %s" % (literal))
        cocci.include_match(False)
elif value == 2**32 - 1 or value == 2**31 - 1 or value == 2**24 - 1 or value == 2**16 - 1 or value == 2**8 - 1:
        print("Skipping 0x%x for cleanup elsewhere" % (value))
        cocci.include_match(False)
elif value & (value + 1) != 0:
        print("Skipping 0x%x because it's not a power of two minus one" % (value))
        cocci.include_match(False)
elif literal.startswith('0x'):
        coccinelle.RESULT = cocci.make_expr("0x%x" % (value + 1))
else:
        coccinelle.RESULT = cocci.make_expr("%d" % (value + 1))

// Replace the literal mask with the calculated result.
@plus_one@
expression literal_mask.LITERAL;
position literal_mask.p;
expression add_one.RESULT;
identifier FUNC;
@@

-       (FUNC()@p & (LITERAL))
+       prandom_u32_max(RESULT)

@collapse_ret@
type T;
identifier VAR;
expression E;
@@

 {
-       T VAR;
-       VAR = (E);
-       return VAR;
+       return E;
 }

@drop_var@
type T;
identifier VAR;
@@

 {
-       T VAR;
        ... when != VAR
 }

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: KP Singh <kpsingh@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz> # for ext4 and sbitmap
Reviewed-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com> # for drbd
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Heiko Carstens <hca@linux.ibm.com> # for s390
Acked-by: Ulf Hansson <ulf.hansson@linaro.org> # for mmc
Acked-by: Darrick J. Wong <djwong@kernel.org> # for xfs
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
2022-10-11 17:42:55 -06:00
..
irqflag-debug.c lockdep: Noinstr annotate warn_bogus_irq_restore() 2021-02-10 14:44:39 +01:00
lock_events.c
lock_events.h
lock_events_list.h locking/rwsem: Remove reader optimistic spinning 2020-12-09 17:08:48 +01:00
lockdep.c locking/lockdep: Print more debug information - report name and key when look_up_lock_class() got confused 2022-09-21 09:58:21 +02:00
lockdep_internals.h locking/lockdep: Iterate lock_classes directly when reading lockdep files 2022-02-16 15:57:58 +01:00
lockdep_proc.c locking/lockdep: Iterate lock_classes directly when reading lockdep files 2022-02-16 15:57:58 +01:00
lockdep_states.h
locktorture.c locktorture,rcutorture,torture: Always log error message 2021-12-07 16:36:17 -08:00
Makefile kmsan: disable instrumentation of unsupported common kernel code 2022-10-03 14:03:20 -07:00
mcs_spinlock.h locking: Fix typos in comments 2021-03-22 02:45:52 +01:00
mutex-debug.c locking/ww_mutex: Gather mutex_waiter initialization 2021-08-17 19:04:41 +02:00
mutex.c locking/mutex: Make contention tracepoints more consistent wrt adaptive spinning 2022-04-05 10:24:36 +02:00
mutex.h locking/mutex: Move the 'struct mutex_waiter' definition from <linux/mutex.h> to the internal header 2021-08-17 18:24:31 +02:00
osq_lock.c locking: Fix typos in comments 2021-03-22 02:45:52 +01:00
percpu-rwsem.c locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked() 2022-08-30 10:56:23 +02:00
qrwlock.c locking: Add __lockfunc to slow path functions 2022-08-19 19:47:51 +02:00
qspinlock.c locking: Add __lockfunc to slow path functions 2022-08-19 19:47:51 +02:00
qspinlock_paravirt.h locking: Add __lockfunc to slow path functions 2022-08-19 19:47:51 +02:00
qspinlock_stat.h
rtmutex.c locking: Apply contention tracepoints in the slow path 2022-04-05 10:24:35 +02:00
rtmutex_api.c locking/rtmutex: Add rt_mutex_lock_nest_lock() and rt_mutex_lock_killable(). 2021-12-04 10:56:23 +01:00
rtmutex_common.h locking/rtmutex: Dont dereference waiter lockless 2021-08-25 15:42:32 +02:00
rwbase_rt.c locking: Apply contention tracepoints in the slow path 2022-04-05 10:24:35 +02:00
rwsem.c locking/rwsem: Disable preemption while trying for rwsem lock 2022-09-15 16:14:02 +02:00
semaphore.c locking: Add __sched to semaphore functions 2022-09-15 16:14:03 +02:00
spinlock.c locking/spinlocks: Mark spinlocks noinline when inline spinlocks are disabled 2022-08-04 11:05:43 +02:00
spinlock_debug.c locking/rwlock: Provide RT variant 2021-08-17 17:50:51 +02:00
spinlock_rt.c locking/rwlocks: introduce write_lock_nested 2022-01-22 08:33:37 +02:00
test-ww_mutex.c treewide: use prandom_u32_max() when possible, part 1 2022-10-11 17:42:55 -06:00
ww_mutex.h locking/ww_mutex: Add rt_mutex based lock type and accessors 2021-08-17 19:05:11 +02:00
ww_rt_mutex.c kernel/locking: Use a pointer in ww_mutex_trylock(). 2021-11-17 14:48:49 +01:00