radix-tree: Partially disable memcg accounting in radix_tree_node_alloc()
Having no preload, which turns accounting off for non-rt kernels, trying to
allocate coming from shmem_fault() when memcg is full sends us scurrying off
to pagefault_out_of_memory(), with dramatic (usually terminal) consequences.
LTP's madvise06 testcase triggers this quite well, and per gitk, the below
was the beginning of RT memcg woes.
58e698af4c63 radix-tree: account radix_tree_node to memory cgroup
Turn memcg accounting off for RT in the problematic path.
Signed-off-by: Mike Galbraith <efault@xxxxxx>
Cc: stable-rt@xxxxxxxxxxxxxxx # +v4.6-rt
---
lib/radix-tree.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -303,6 +303,13 @@ radix_tree_node_alloc(struct radix_tree_
if (!gfpflags_allow_blocking(gfp_mask) && !in_interrupt()) {
struct radix_tree_preload *rtp;
+#if defined(CONFIG_PREEMPT_RT_FULL) && defined(CONFIG_MEMCG)
+ /*
+ * Arriving here from shmem_fault() and meeting a full memcg
+ * will send us to pagefault_out_of_memory(), and a dead box.
+ */
+ gfp_mask &= ~__GFP_ACCOUNT;
+#endif
/*
* Even if the caller has preloaded, try to allocate from the
* cache first for the new node to get accounted to the memory
--
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