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| author |   Davidlohr Bueso <dave@stgolabs.net> | 2021-02-26 09:50:26 -0800 |
|---|---|---|
| committer |   Thomas Gleixner <tglx@linutronix.de> | 2021-03-11 19:19:17 +0100 |
| commit | 9a4b99fce659c03699f1cb5003ebe7c57c084d49 (patch) | |
| tree | 7f5d448c069f69d96b3f0bad4b6d19ae80509708 /kernel/futex.c | |
| parent | ath10k: Detect conf_mutex held ath10k_drain_tx() calls (diff) | |
| download | linux-dev-9a4b99fce659c03699f1cb5003ebe7c57c084d49.tar.xz linux-dev-9a4b99fce659c03699f1cb5003ebe7c57c084d49.zip | |
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.c | 7 |
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 |