@@ -19,6 +19,12 @@
#include "util.h"
+/*
+ * The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
+ */
+static void free_ipc(struct work_struct *unused);
+static DECLARE_WORK(free_ipc_work, free_ipc);
+
static struct ucounts *inc_ipc_namespaces(struct user_namespace *ns)
{
return inc_ucount(ns, current_euid(), UCOUNT_IPC_NAMESPACES);
@@ -37,9 +43,18 @@ static struct ipc_namespace *create_ipc_ns(struct user_namespace *user_ns,
int err;
err = -ENOSPC;
+ again:
ucounts = inc_ipc_namespaces(user_ns);
- if (!ucounts)
+ if (!ucounts) {
+ /*
+ * IPC namespaces are freed asynchronously, by free_ipc_work.
+ * If frees were pending, flush_work will wait, and
+ * return true. Fail the allocation if no frees are pending.
+ */
+ if (flush_work(&free_ipc_work))
+ goto again;
goto fail;
+ }
err = -ENOMEM;
ns = kzalloc(sizeof(struct ipc_namespace), GFP_KERNEL_ACCOUNT);
@@ -157,11 +172,6 @@ static void free_ipc(struct work_struct *unused)
free_ipc_ns(n);
}
-/*
- * The work queue is used to avoid the cost of synchronize_rcu in kern_unmount.
- */
-static DECLARE_WORK(free_ipc_work, free_ipc);
-
/*
* put_ipc_ns - drop a reference to an ipc namespace.
* @ns: the namespace to put
Currently the ipc namespace allocation will fail when there are ipc_namespace structures pending to be freed. This results in the simple test case below, as well as some real world workloads, to get allocation failures even when the number of ipc namespaces in actual use is way below the limit. int main() { int i; for (i = 0; i < 100000; i++) { if (unshare(CLONE_NEWIPC) < 0) error(EXIT_FAILURE, errno, "unshare"); } } Make the allocation of an ipc_namespace wait for pending frees, so it will succeed. real 6m19.197s user 0m0.041s sys 0m1.019s Signed-off-by: Rik van Riel <riel@surriel.com> Reported-by: Chris Mason <clm@meta.com> --- ipc/namespace.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-)