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authorDavidlohr Bueso <dave@stgolabs.net>2021-02-26 20:50:26 +0300
committerThomas Gleixner <tglx@linutronix.de>2021-03-11 21:19:17 +0300
commit9a4b99fce659c03699f1cb5003ebe7c57c084d49 (patch)
tree7f5d448c069f69d96b3f0bad4b6d19ae80509708 /kernel/futex.c
parentbdb1050ee1faaec1e78c15de8b1959176f26c655 (diff)
downloadlinux-9a4b99fce659c03699f1cb5003ebe7c57c084d49.tar.xz
kernel/futex: Kill rt_mutex_next_owner()
Update wake_futex_pi() and kill the call altogether. This is possible because: (i) The case of fixup_owner() in which the pi_mutex was stolen from the signaled enqueued top-waiter which fails to trylock and doesn't see a current owner of the rtmutex but needs to acknowledge an non-enqueued higher priority waiter, which is the other alternative. This used to be handled by rt_mutex_next_owner(), which guaranteed fixup_pi_state_owner('newowner') never to be nil. Nowadays the logic is handled by an EAGAIN loop, without the need of rt_mutex_next_owner(). Specifically: c1e2f0eaf015 (futex: Avoid violating the 10th rule of futex) 9f5d1c336a10 (futex: Handle transient "ownerless" rtmutex state correctly) (ii) rt_mutex_next_owner() and rt_mutex_top_waiter() are semantically equivalent, as of: c28d62cf52d7 (locking/rtmutex: Handle non enqueued waiters gracefully in remove_waiter()) So instead of keeping the call around, just use the good ole rt_mutex_top_waiter(). No change in semantics. Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/20210226175029.50335-1-dave@stgolabs.net
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c7
1 files changed, 5 insertions, 2 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index e68db7745039..db8002dbca7a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1494,13 +1494,14 @@ static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
{
u32 curval, newval;
+ struct rt_mutex_waiter *top_waiter;
struct task_struct *new_owner;
bool postunlock = false;
DEFINE_WAKE_Q(wake_q);
int ret = 0;
- new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
- if (WARN_ON_ONCE(!new_owner)) {
+ top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
+ if (WARN_ON_ONCE(!top_waiter)) {
/*
* As per the comment in futex_unlock_pi() this should not happen.
*
@@ -1513,6 +1514,8 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
goto out_unlock;
}
+ new_owner = top_waiter->task;
+
/*
* We pass it to the next owner. The WAITERS bit is always kept
* enabled while there is PI state around. We cleanup the owner