Commit 02b07bde authored by Linus Torvalds's avatar Linus Torvalds

Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull locking fixes from Ingo Molnar:
 "Misc fixes:

   - a file-based futex fix
   - one more spin_unlock_wait() fix
   - a ww-mutex deadlock detection improvement/fix
   - and a raw_read_seqcount_latch() barrier fix"

* 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  futex: Calculate the futex key based on a tail page for file-based futexes
  locking/qspinlock: Fix spin_unlock_wait() some more
  locking/ww_mutex: Report recursive ww_mutex locking early
  locking/seqcount: Re-fix raw_read_seqcount_latch()
parents 606c17f4 077fa7ae
......@@ -21,38 +21,34 @@
#include <asm-generic/qspinlock_types.h>
/**
* queued_spin_unlock_wait - wait until the _current_ lock holder releases the lock
* @lock : Pointer to queued spinlock structure
*
* There is a very slight possibility of live-lock if the lockers keep coming
* and the waiter is just unfortunate enough to not see any unlock state.
*/
#ifndef queued_spin_unlock_wait
extern void queued_spin_unlock_wait(struct qspinlock *lock);
#endif
/**
* queued_spin_is_locked - is the spinlock locked?
* @lock: Pointer to queued spinlock structure
* Return: 1 if it is locked, 0 otherwise
*/
#ifndef queued_spin_is_locked
static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
{
/*
* queued_spin_lock_slowpath() can ACQUIRE the lock before
* issuing the unordered store that sets _Q_LOCKED_VAL.
*
* See both smp_cond_acquire() sites for more detail.
*
* This however means that in code like:
*
* spin_lock(A) spin_lock(B)
* spin_unlock_wait(B) spin_is_locked(A)
* do_something() do_something()
*
* Both CPUs can end up running do_something() because the store
* setting _Q_LOCKED_VAL will pass through the loads in
* spin_unlock_wait() and/or spin_is_locked().
* See queued_spin_unlock_wait().
*
* Avoid this by issuing a full memory barrier between the spin_lock()
* and the loads in spin_unlock_wait() and spin_is_locked().
*
* Note that regular mutual exclusion doesn't care about this
* delayed store.
* Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
* isn't immediately observable.
*/
smp_mb();
return atomic_read(&lock->val) & _Q_LOCKED_MASK;
return atomic_read(&lock->val);
}
#endif
/**
* queued_spin_value_unlocked - is the spinlock structure unlocked?
......@@ -122,21 +118,6 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
}
#endif
/**
* queued_spin_unlock_wait - wait until current lock holder releases the lock
* @lock : Pointer to queued spinlock structure
*
* There is a very slight possibility of live-lock if the lockers keep coming
* and the waiter is just unfortunate enough to not see any unlock state.
*/
static inline void queued_spin_unlock_wait(struct qspinlock *lock)
{
/* See queued_spin_is_locked() */
smp_mb();
while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
cpu_relax();
}
#ifndef virt_spin_lock
static __always_inline bool virt_spin_lock(struct qspinlock *lock)
{
......
......@@ -277,7 +277,10 @@ static inline void raw_write_seqcount_barrier(seqcount_t *s)
static inline int raw_read_seqcount_latch(seqcount_t *s)
{
return lockless_dereference(s)->sequence;
int seq = READ_ONCE(s->sequence);
/* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
smp_read_barrier_depends();
return seq;
}
/**
......@@ -331,7 +334,7 @@ static inline int raw_read_seqcount_latch(seqcount_t *s)
* unsigned seq, idx;
*
* do {
* seq = lockless_dereference(latch)->seq;
* seq = raw_read_seqcount_latch(&latch->seq);
*
* idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...);
......
......@@ -469,7 +469,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
{
unsigned long address = (unsigned long)uaddr;
struct mm_struct *mm = current->mm;
struct page *page;
struct page *page, *tail;
struct address_space *mapping;
int err, ro = 0;
......@@ -530,7 +530,15 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
* considered here and page lock forces unnecessarily serialization
* From this point on, mapping will be re-verified if necessary and
* page lock will be acquired only if it is unavoidable
*/
*
* Mapping checks require the head page for any compound page so the
* head page and mapping is looked up now. For anonymous pages, it
* does not matter if the page splits in the future as the key is
* based on the address. For filesystem-backed pages, the tail is
* required as the index of the page determines the key. For
* base pages, there is no tail page and tail == page.
*/
tail = page;
page = compound_head(page);
mapping = READ_ONCE(page->mapping);
......@@ -654,7 +662,7 @@ get_futex_key(u32 __user *uaddr, int fshared, union futex_key *key, int rw)
key->both.offset |= FUT_OFF_INODE; /* inode-based key */
key->shared.inode = inode;
key->shared.pgoff = basepage_index(page);
key->shared.pgoff = basepage_index(tail);
rcu_read_unlock();
}
......
......@@ -486,9 +486,6 @@ __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
if (!hold_ctx)
return 0;
if (unlikely(ctx == hold_ctx))
return -EALREADY;
if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
(ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
#ifdef CONFIG_DEBUG_MUTEXES
......@@ -514,6 +511,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
unsigned long flags;
int ret;
if (use_ww_ctx) {
struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
return -EALREADY;
}
preempt_disable();
mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
......
......@@ -267,6 +267,66 @@ static __always_inline u32 __pv_wait_head_or_lock(struct qspinlock *lock,
#define queued_spin_lock_slowpath native_queued_spin_lock_slowpath
#endif
/*
* queued_spin_lock_slowpath() can (load-)ACQUIRE the lock before
* issuing an _unordered_ store to set _Q_LOCKED_VAL.
*
* This means that the store can be delayed, but no later than the
* store-release from the unlock. This means that simply observing
* _Q_LOCKED_VAL is not sufficient to determine if the lock is acquired.
*
* There are two paths that can issue the unordered store:
*
* (1) clear_pending_set_locked(): *,1,0 -> *,0,1
*
* (2) set_locked(): t,0,0 -> t,0,1 ; t != 0
* atomic_cmpxchg_relaxed(): t,0,0 -> 0,0,1
*
* However, in both cases we have other !0 state we've set before to queue
* ourseves:
*
* For (1) we have the atomic_cmpxchg_acquire() that set _Q_PENDING_VAL, our
* load is constrained by that ACQUIRE to not pass before that, and thus must
* observe the store.
*
* For (2) we have a more intersting scenario. We enqueue ourselves using
* xchg_tail(), which ends up being a RELEASE. This in itself is not
* sufficient, however that is followed by an smp_cond_acquire() on the same
* word, giving a RELEASE->ACQUIRE ordering. This again constrains our load and
* guarantees we must observe that store.
*
* Therefore both cases have other !0 state that is observable before the
* unordered locked byte store comes through. This means we can use that to
* wait for the lock store, and then wait for an unlock.
*/
#ifndef queued_spin_unlock_wait
void queued_spin_unlock_wait(struct qspinlock *lock)
{
u32 val;
for (;;) {
val = atomic_read(&lock->val);
if (!val) /* not locked, we're done */
goto done;
if (val & _Q_LOCKED_MASK) /* locked, go wait for unlock */
break;
/* not locked, but pending, wait until we observe the lock */
cpu_relax();
}
/* any unlock is good */
while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
cpu_relax();
done:
smp_rmb(); /* CTRL + RMB -> ACQUIRE */
}
EXPORT_SYMBOL(queued_spin_unlock_wait);
#endif
#endif /* _GEN_PV_LOCK_SLOWPATH */
/**
......
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