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Revert "jump_label: Fix concurrency issues in static_key_slow_dec()"

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This reverts commit 6b8ccab544 which is
commit 83ab38ef0a0b2407d43af9575bb32333fdd74fb2 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Ie36013c12e969a77b3f68bd37a3b4caab877d593
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Greg Kroah-Hartman
2024-09-12 13:51:23 +00:00
parent 81c0bf47a8
commit 7c3cc07862
1 changed files with 16 additions and 29 deletions
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45
kernel/jump_label.c
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@@ -131,7 +131,7 @@ bool static_key_fast_inc_not_disabled(struct static_key *key)
STATIC_KEY_CHECK_USE(key); STATIC_KEY_CHECK_USE(key);
/* /*
* Negative key->enabled has a special meaning: it sends * Negative key->enabled has a special meaning: it sends
* static_key_slow_inc/dec() down the slow path, and it is non-zero * static_key_slow_inc() down the slow path, and it is non-zero
* so it counts as "enabled" in jump_label_update(). Note that * so it counts as "enabled" in jump_label_update(). Note that
* atomic_inc_unless_negative() checks >= 0, so roll our own. * atomic_inc_unless_negative() checks >= 0, so roll our own.
*/ */
@@ -150,7 +150,7 @@ bool static_key_slow_inc_cpuslocked(struct static_key *key)
lockdep_assert_cpus_held(); lockdep_assert_cpus_held();
/* /*
* Careful if we get concurrent static_key_slow_inc/dec() calls; * Careful if we get concurrent static_key_slow_inc() calls;
* later calls must wait for the first one to _finish_ the * later calls must wait for the first one to _finish_ the
* jump_label_update() process. At the same time, however, * jump_label_update() process. At the same time, however,
* the jump_label_update() call below wants to see * the jump_label_update() call below wants to see
@@ -247,32 +247,20 @@ EXPORT_SYMBOL_GPL(static_key_disable);
static bool static_key_slow_try_dec(struct static_key *key) static bool static_key_slow_try_dec(struct static_key *key)
{ {
int v; int val;
val = atomic_fetch_add_unless(&key->enabled, -1, 1);
if (val == 1)
return false;
/* /*
* Go into the slow path if key::enabled is less than or equal than * The negative count check is valid even when a negative
* one. One is valid to shut down the key, anything less than one * key->enabled is in use by static_key_slow_inc(); a
* is an imbalance, which is handled at the call site. * __static_key_slow_dec() before the first static_key_slow_inc()
* * returns is unbalanced, because all other static_key_slow_inc()
* That includes the special case of '-1' which is set in * instances block while the update is in progress.
* static_key_slow_inc_cpuslocked(), but that's harmless as it is
* fully serialized in the slow path below. By the time this task
* acquires the jump label lock the value is back to one and the
* retry under the lock must succeed.
*/ */
v = atomic_read(&key->enabled); WARN(val < 0, "jump label: negative count!\n");
do {
/*
* Warn about the '-1' case though; since that means a
* decrement is concurrent with a first (0->1) increment. IOW
* people are trying to disable something that wasn't yet fully
* enabled. This suggests an ordering problem on the user side.
*/
WARN_ON_ONCE(v < 0);
if (v <= 1)
return false;
} while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v - 1)));
return true; return true;
} }
@@ -283,11 +271,10 @@ static void __static_key_slow_dec_cpuslocked(struct static_key *key)
if (static_key_slow_try_dec(key)) if (static_key_slow_try_dec(key))
return; return;
guard(mutex)(&jump_label_mutex); jump_label_lock();
if (atomic_cmpxchg(&key->enabled, 1, 0)) if (atomic_dec_and_test(&key->enabled))
jump_label_update(key); jump_label_update(key);
else jump_label_unlock();
WARN_ON_ONCE(!static_key_slow_try_dec(key));
} }
static void __static_key_slow_dec(struct static_key *key) static void __static_key_slow_dec(struct static_key *key)