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Close a race condition where if we were obtaining a sleep lock and no spin

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locks were held, we could be preempted and switch CPU's in between the time
that we set a variable to the list of spin locks on our CPU and the time
that we checked that variable to ensure no spinlocks were held while
grabbing a sleep lock.  Losing the race resulted in checking some other
CPU's spin lock list and bogusly panicing.
This commit is contained in:
John Baldwin 2001-03-28 16:11:51 +00:00
parent 249932144b
commit 026e76f43e
1 changed files with 14 additions and 1 deletions
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15
sys/kern/subr_witness.c
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@ -471,13 +471,26 @@ witness_lock(struct lock_object *lock, int flags, const char *file, int line)
return;
}
/*
* We have to hold a spinlock to keep lock_list valid across the check
* in the LC_SLEEPLOCK case. In the LC_SPINLOCK case, it is already
* protected by the spinlock we are currently performing the witness
* checks on, so it is ok to release the lock after performing this
* check. All we have to protect is the LC_SLEEPLOCK case when no
* spinlocks are held as we may get preempted during this check and
* lock_list could end up pointing to some other CPU's spinlock list.
*/
mtx_lock_spin(&w_mtx);
lock_list = PCPU_PTR(spinlocks);
if (class->lc_flags & LC_SLEEPLOCK) {
if (*lock_list != NULL)
if (*lock_list != NULL) {
mtx_unlock_spin(&w_mtx);
panic("blockable sleep lock (%s) %s @ %s:%d",
class->lc_name, lock->lo_name, file, line);
}
lock_list = &p->p_sleeplocks;
}
mtx_unlock_spin(&w_mtx);
if (flags & LOP_TRYLOCK)
goto out;