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futex: Remove pointless mmgrap() + mmdrop()

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We always set 'key->private.mm' to 'current->mm', getting an extra
reference on 'current->mm' is quite pointless, because as long as the
task is blocked it isn't going to go away.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This commit is contained in:
Peter Zijlstra 2020-03-04 13:02:41 +01:00
parent 3867913c45
commit 222993395e
1 changed files with 1 additions and 13 deletions
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14
kernel/futex.c
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@ -331,17 +331,6 @@ static void compat_exit_robust_list(struct task_struct *curr);
static inline void compat_exit_robust_list(struct task_struct *curr) { }
#endif
static inline void futex_get_mm(union futex_key *key)
{
mmgrab(key->private.mm);
/*
* Ensure futex_get_mm() implies a full barrier such that
* get_futex_key() implies a full barrier. This is relied upon
* as smp_mb(); (B), see the ordering comment above.
*/
smp_mb__after_atomic();
}
/*
* Reflects a new waiter being added to the waitqueue.
*/
@ -432,7 +421,7 @@ static void get_futex_key_refs(union futex_key *key)
smp_mb(); /* explicit smp_mb(); (B) */
break;
case FUT_OFF_MMSHARED:
futex_get_mm(key); /* implies smp_mb(); (B) */
smp_mb(); /* explicit smp_mb(); (B) */
break;
default:
/*
@ -465,7 +454,6 @@ static void drop_futex_key_refs(union futex_key *key)
case FUT_OFF_INODE:
break;
case FUT_OFF_MMSHARED:
mmdrop(key->private.mm);
break;
}
}