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BACKPORT: rtmutex: Use waiter::task instead of current in remove_waiter()

Browse source 
remove_waiter() is used by the slowlock paths, but it is also used for
proxy-lock rollback in rt_mutex_start_proxy_lock() when invoked from
futex_requeue().

In the latter case waiter::task is not current, but remove_waiter()
operates on current for the dequeue operation. That results in several
problems:

  1) the rbtree dequeue happens without waiter::task::pi_lock being held

  2) the waiter task's pi_blocked_on state is not cleared, which leaves a
     dangling pointer primed for UAF around.

  3) rt_mutex_adjust_prio_chain() operates on the wrong top priority waiter
     task

Use waiter::task instead of current in all related operations in
remove_waiter() to cure those problems.

[ tglx: Fixup rt_mutex_adjust_prio_chain(), add a comment and amend the
  	changelog ]

Fixes: 8161239a8b ("rtmutex: Simplify PI algorithm and make highest prio task get lock")
Change-Id: I3ff8da2830773e04f55828b11c9d461ab6ee57c5
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Signed-off-by: Keenan Dong <keenanat2000@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Cc: stable@vger.kernel.org
[Tashar02: Open-code scoped_guard() on msm-5.4]
Signed-off-by: Tashfin Shakeer Rhythm <tashfinshakeerrhythm@gmail.com>
This commit is contained in:
Keenan Dong 2026-04-08 16:46:00 +08:00 • committed by Tashfin Shakeer Rhythm
commit 6efbfed641
No known key found for this signature in database
GPG key ID: 02FFCB5954E9A100
1 changed files with 7 additions and 4 deletions
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11
kernel/locking/rtmutex.c
View file

@ -1063,20 +1063,23 @@ static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
*
* Must be called with lock->wait_lock held and interrupts disabled. I must
* have just failed to try_to_take_rt_mutex().
*
* When invoked from rt_mutex_start_proxy_lock() waiter::task != current !
*/
static void remove_waiter(struct rt_mutex *lock,
struct rt_mutex_waiter *waiter)
{
bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
struct task_struct *owner = rt_mutex_owner(lock);
struct task_struct *waiter_task = waiter->task;
struct rt_mutex *next_lock;
lockdep_assert_held(&lock->wait_lock);
raw_spin_lock(&current->pi_lock);
raw_spin_lock(&waiter_task->pi_lock);
rt_mutex_dequeue(lock, waiter);
current->pi_blocked_on = NULL;
raw_spin_unlock(&current->pi_lock);
waiter_task->pi_blocked_on = NULL;
raw_spin_unlock(&waiter_task->pi_lock);
/*
* Only update priority if the waiter was the highest priority
@ -1112,7 +1115,7 @@ static void remove_waiter(struct rt_mutex *lock,
raw_spin_unlock_irq(&lock->wait_lock);
rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
next_lock, NULL, current);
next_lock, NULL, waiter_task);
raw_spin_lock_irq(&lock->wait_lock);
}