Author: jamie
Date: Thu Jun 9 16:41:41 2016
New Revision: 301745
URL: https://svnweb.freebsd.org/changeset/base/301745
Log:
Make sure the OSD methods for jail set and remove can't run concurrently,
by holding allprison_lock exclusively (even if only for a moment before
downgrading) on all paths that call PR_METHOD_REMOVE. Since they may run
on a downgraded lock, it's still possible for them to run concurrently
with PR_METHOD_GET, which will need to use the prison lock.
Modified:
head/sys/kern/kern_jail.c
Modified: head/sys/kern/kern_jail.c
==============================================================================
--- head/sys/kern/kern_jail.c Thu Jun 9 16:30:27 2016 (r301744)
+++ head/sys/kern/kern_jail.c Thu Jun 9 16:41:41 2016 (r301745)
@@ -2383,7 +2383,14 @@ sys_jail_attach(struct thread *td, struc
if (error)
return (error);
- sx_slock(&allprison_lock);
+ /*
+ * Start with exclusive hold on allprison_lock to ensure that a possible
+ * PR_METHOD_REMOVE call isn't concurrent with jail_set or jail_remove.
+ * But then immediately downgrade it since we don't need to stop
+ * readers.
+ */
+ sx_xlock(&allprison_lock);
+ sx_downgrade(&allprison_lock);
pr = prison_find_child(td->td_ucred->cr_prison, uap->jid);
if (pr == NULL) {
sx_sunlock(&allprison_lock);
@@ -2601,9 +2608,11 @@ prison_complete(void *context, int pendi
{
struct prison *pr = context;
+ sx_xlock(&allprison_lock);
mtx_lock(&pr->pr_mtx);
prison_deref(pr, pr->pr_uref
- ? PD_DEREF | PD_DEUREF | PD_LOCKED : PD_LOCKED);
+ ? PD_DEREF | PD_DEUREF | PD_LOCKED | PD_LIST_XLOCKED
+ : PD_LOCKED | PD_LIST_XLOCKED);
}
/*
@@ -2647,13 +2656,8 @@ prison_deref(struct prison *pr, int flag
*/
if (lasturef) {
if (!(flags & (PD_LIST_SLOCKED | PD_LIST_XLOCKED))) {
- if (ref > 1) {
- sx_slock(&allprison_lock);
- flags |= PD_LIST_SLOCKED;
- } else {
- sx_xlock(&allprison_lock);
- flags |= PD_LIST_XLOCKED;
- }
+ sx_xlock(&allprison_lock);
+ flags |= PD_LIST_XLOCKED;
}
(void)osd_jail_call(pr, PR_METHOD_REMOVE, NULL);
mtx_lock(&pr->pr_mtx);
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