123 lines
4.1 KiB
Diff
123 lines
4.1 KiB
Diff
From 5a3649e609ba5a5e6765d0a3b13a126020f03d8e Mon Sep 17 00:00:00 2001
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From: Peter Zijlstra <peterz@infradead.org>
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Date: Wed, 6 Jun 2018 15:31:26 +0200
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Subject: [PATCH 343/365] futex: Fix pi_state->owner serialization
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[ Upstream commit c74aef2d06a9f59cece89093eecc552933cba72a ]
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There was a reported suspicion about a race between exit_pi_state_list()
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and put_pi_state(). The same report mentioned the comment with
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put_pi_state() said it should be called with hb->lock held, and it no
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longer is in all places.
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As it turns out, the pi_state->owner serialization is indeed broken. As per
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the new rules:
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734009e96d19 ("futex: Change locking rules")
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pi_state->owner should be serialized by pi_state->pi_mutex.wait_lock.
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For the sites setting pi_state->owner we already hold wait_lock (where
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required) but exit_pi_state_list() and put_pi_state() were not and
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raced on clearing it.
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Fixes: 734009e96d19 ("futex: Change locking rules")
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Reported-by: Gratian Crisan <gratian.crisan@ni.com>
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Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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Cc: dvhart@infradead.org
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Cc: stable@vger.kernel.org
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Link: https://lkml.kernel.org/r/20170922154806.jd3ffltfk24m4o4y@hirez.programming.kicks-ass.net
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Signed-off-by: Julia Cartwright <julia@ni.com>
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---
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kernel/futex.c | 34 ++++++++++++++++++++++------------
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1 file changed, 22 insertions(+), 12 deletions(-)
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diff --git a/kernel/futex.c b/kernel/futex.c
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index 8df43644f88d..8b01a19e3260 100644
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--- a/kernel/futex.c
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+++ b/kernel/futex.c
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@@ -836,8 +836,6 @@ static void get_pi_state(struct futex_pi_state *pi_state)
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/*
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* Drops a reference to the pi_state object and frees or caches it
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* when the last reference is gone.
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- *
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- * Must be called with the hb lock held.
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*/
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static void put_pi_state(struct futex_pi_state *pi_state)
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{
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@@ -852,16 +850,22 @@ static void put_pi_state(struct futex_pi_state *pi_state)
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* and has cleaned up the pi_state already
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*/
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if (pi_state->owner) {
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- raw_spin_lock_irq(&pi_state->owner->pi_lock);
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- list_del_init(&pi_state->list);
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- raw_spin_unlock_irq(&pi_state->owner->pi_lock);
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+ struct task_struct *owner;
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- rt_mutex_proxy_unlock(&pi_state->pi_mutex, pi_state->owner);
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+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
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+ owner = pi_state->owner;
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+ if (owner) {
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+ raw_spin_lock(&owner->pi_lock);
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+ list_del_init(&pi_state->list);
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+ raw_spin_unlock(&owner->pi_lock);
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+ }
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+ rt_mutex_proxy_unlock(&pi_state->pi_mutex, owner);
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+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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}
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- if (current->pi_state_cache)
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+ if (current->pi_state_cache) {
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kfree(pi_state);
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- else {
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+ } else {
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/*
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* pi_state->list is already empty.
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* clear pi_state->owner.
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@@ -920,14 +924,15 @@ void exit_pi_state_list(struct task_struct *curr)
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raw_spin_unlock_irq(&curr->pi_lock);
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spin_lock(&hb->lock);
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-
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- raw_spin_lock_irq(&curr->pi_lock);
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+ raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
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+ raw_spin_lock(&curr->pi_lock);
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/*
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* We dropped the pi-lock, so re-check whether this
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* task still owns the PI-state:
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*/
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if (head->next != next) {
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- raw_spin_unlock_irq(&curr->pi_lock);
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+ raw_spin_unlock(&curr->pi_lock);
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+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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spin_unlock(&hb->lock);
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raw_spin_lock_irq(&curr->pi_lock);
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continue;
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@@ -937,9 +942,10 @@ void exit_pi_state_list(struct task_struct *curr)
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WARN_ON(list_empty(&pi_state->list));
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list_del_init(&pi_state->list);
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pi_state->owner = NULL;
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- raw_spin_unlock_irq(&curr->pi_lock);
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+ raw_spin_unlock(&curr->pi_lock);
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get_pi_state(pi_state);
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+ raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
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spin_unlock(&hb->lock);
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rt_mutex_futex_unlock(&pi_state->pi_mutex);
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@@ -1221,6 +1227,10 @@ static int attach_to_pi_owner(u32 uval, union futex_key *key,
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WARN_ON(!list_empty(&pi_state->list));
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list_add(&pi_state->list, &p->pi_state_list);
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+ /*
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+ * Assignment without holding pi_state->pi_mutex.wait_lock is safe
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+ * because there is no concurrency as the object is not published yet.
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+ */
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pi_state->owner = p;
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raw_spin_unlock_irq(&p->pi_lock);
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--
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2.28.0
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