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jail: Clean up some function placement and improve comments.

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Move prison_hold, prison_hold_locked ,prison_proc_hold, and
prison_proc_free to a more intuitive part of the file (together with
with prison_free and prison_free_locked), and add or improve comments
to these and others, to better describe what's going in the prison
reference cycle.

No functional changes.
This commit is contained in:
Jamie Gritton 2021-01-18 17:23:51 -08:00
parent a45d905616
commit effad35ed1
1 changed files with 96 additions and 61 deletions
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157
sys/kern/kern_jail.c
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@ -2604,8 +2604,35 @@ prison_allow(struct ucred *cred, unsigned flag)
}
/*
* Remove a prison reference. If that was the last reference, remove the
* prison itself - but not in this context in case there are locks held.
* Hold a prison reference, by incrementing pr_ref. It is generally
* an error to hold a prison that does not already have a reference.
* A prison record will remain valid as long as it has at least one
* reference, and will not be removed as long as either the prison
* mutex or the allprison lock is held (allprison_lock may be shared).
*/
void
prison_hold_locked(struct prison *pr)
{
mtx_assert(&pr->pr_mtx, MA_OWNED);
KASSERT(pr->pr_ref > 0,
("Trying to hold dead prison %p (jid=%d).", pr, pr->pr_id));
pr->pr_ref++;
}
void
prison_hold(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
prison_hold_locked(pr);
mtx_unlock(&pr->pr_mtx);
}
/*
* Remove a prison reference. If that was the last reference, the
* prison will be removed (at a later time). Return with the prison
* unlocked.
*/
void
prison_free_locked(struct prison *pr)
@ -2615,8 +2642,13 @@ prison_free_locked(struct prison *pr)
mtx_assert(&pr->pr_mtx, MA_OWNED);
ref = --pr->pr_ref;
mtx_unlock(&pr->pr_mtx);
if (ref == 0)
if (ref == 0) {
/*
* Don't remove the last reference in this context,
* in case there are locks held.
*/
taskqueue_enqueue(taskqueue_thread, &pr->pr_task);
}
}
void
@ -2627,6 +2659,54 @@ prison_free(struct prison *pr)
prison_free_locked(pr);
}
/*
* Hold a a prison for user visibility, by incrementing pr_uref.
* It is generally an error to hold a prison that isn't already
* user-visible, except through the the jail system calls. It is also
* an error to hold an invalid prison. A prison record will remain
* alive as long as it has at least one user reference, and will not
* be set to the dying state was long as the prison mutex is held.
*/
void
prison_proc_hold(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
KASSERT(pr->pr_uref > 0,
("Cannot add a process to a non-alive prison (jid=%d)", pr->pr_id));
pr->pr_uref++;
mtx_unlock(&pr->pr_mtx);
}
/*
* Remove a prison user reference. If it was the last reference, the
* prison will be considered "dying", and may be removed once all of
* its references are dropped.
*/
void
prison_proc_free(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
KASSERT(pr->pr_uref > 0,
("Trying to kill a process in a dead prison (jid=%d)", pr->pr_id));
if (pr->pr_uref > 1)
pr->pr_uref--;
else {
/*
* Don't remove the last user reference in this context,
* which is expected to be a process that is not only locked,
* but also half dead. Add a reference so any calls to
* prison_free() won't re-submit the task.
*/
pr->pr_ref++;
mtx_unlock(&pr->pr_mtx);
taskqueue_enqueue(taskqueue_thread, &pr->pr_task);
return;
}
mtx_unlock(&pr->pr_mtx);
}
/*
* Complete a call to either prison_free or prison_proc_free.
*/
@ -2637,16 +2717,24 @@ prison_complete(void *context, int pending)
sx_xlock(&allprison_lock);
mtx_lock(&pr->pr_mtx);
prison_deref(pr, pr->pr_uref
/*
* If this is completing a call to prison_proc_free, there will still
* be a user reference held; clear that as well as the reference that
* was added. No references are expected if this is completing a call
* to prison_free, but prison_deref is still called for the cleanup.
*/
prison_deref(pr, pr->pr_uref > 0
? PD_DEREF | PD_DEUREF | PD_LOCKED | PD_LIST_XLOCKED
: PD_LOCKED | PD_LIST_XLOCKED);
}
/*
* Remove a prison reference (usually). This internal version assumes no
* mutexes are held, except perhaps the prison itself. If there are no more
* references, release and delist the prison. On completion, the prison lock
* and the allprison lock are both unlocked.
* Remove a prison reference and/or user reference (usually).
* This assumes context that allows sleeping (for allprison_lock),
* with no non-sleeping locks held, except perhaps the prison itself.
* If there are no more references, release and delist the prison.
* On completion, the prison lock and the allprison lock are both
* unlocked.
*/
static void
prison_deref(struct prison *pr, int flags)
@ -2750,59 +2838,6 @@ prison_deref(struct prison *pr, int flags)
}
}
void
prison_hold_locked(struct prison *pr)
{
mtx_assert(&pr->pr_mtx, MA_OWNED);
KASSERT(pr->pr_ref > 0,
("Trying to hold dead prison %p (jid=%d).", pr, pr->pr_id));
pr->pr_ref++;
}
void
prison_hold(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
prison_hold_locked(pr);
mtx_unlock(&pr->pr_mtx);
}
void
prison_proc_hold(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
KASSERT(pr->pr_uref > 0,
("Cannot add a process to a non-alive prison (jid=%d)", pr->pr_id));
pr->pr_uref++;
mtx_unlock(&pr->pr_mtx);
}
void
prison_proc_free(struct prison *pr)
{
mtx_lock(&pr->pr_mtx);
KASSERT(pr->pr_uref > 0,
("Trying to kill a process in a dead prison (jid=%d)", pr->pr_id));
if (pr->pr_uref > 1)
pr->pr_uref--;
else {
/*
* Don't remove the last user reference in this context, which
* is expected to be a process that is not only locked, but
* also half dead.
*/
pr->pr_ref++;
mtx_unlock(&pr->pr_mtx);
taskqueue_enqueue(taskqueue_thread, &pr->pr_task);
return;
}
mtx_unlock(&pr->pr_mtx);
}
/*
* Set or clear a permission bit in the pr_allow field, passing restrictions
* (cleared permission) down to child jails.