Commit 79dfdaccd1d5 ("memcg: make oom_lock 0 and 1 based rather than counter") tried to oom lock the hierarchy and roll back upon encountering an already locked memcg. The code is confused when it comes to detecting a locked memcg, though, so it would fail and rollback after locking one memcg and encountering an unlocked second one. The result is that oom-locking hierarchies fails unconditionally and that every oom killer invocation simply goes to sleep on the oom waitqueue forever. The tasks practically hang forever without anyone intervening, possibly holding locks that trip up unrelated tasks, too.
Unified · Split
| @@ -1841,29 +1841,23 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, · 1840 unmodified lines | |||
| 1841 | */ | 1841 | */ |
| 1842 | static bool mem_cgroup_oom_lock(struct mem_cgroup *mem) | 1842 | static bool mem_cgroup_oom_lock(struct mem_cgroup *mem) |
| 1843 | { | 1843 | { |
| 1844 | int lock_count = -1; | ||
| 1845 | struct mem_cgroup *iter, *failed = NULL; | 1844 | struct mem_cgroup *iter, *failed = NULL; |
| 1846 | bool cond = true; | 1845 | bool cond = true; |
| 1847 | 1846 | ||
| 1848 | for_each_mem_cgroup_tree_cond(iter, mem, cond) { | 1847 | for_each_mem_cgroup_tree_cond(iter, mem, cond) { |
| 1849 | bool locked = iter->oom_lock; | 1848 | if (iter->oom_lock) { |
| 1850 | |||
| 1851 | iter->oom_lock = true; | ||
| 1852 | if (lock_count == -1) | ||
| 1853 | lock_count = iter->oom_lock; | ||
| 1854 | else if (lock_count != locked) { | ||
| 1855 | /* | 1849 | /* |
| 1856 | * this subtree of our hierarchy is already locked | 1850 | * this subtree of our hierarchy is already locked |
| 1857 | * so we cannot give a lock. | 1851 | * so we cannot give a lock. |
| 1858 | */ | 1852 | */ |
| 1859 | lock_count = 0; | ||
| 1860 | failed = iter; | 1853 | failed = iter; |
| 1861 | cond = false; | 1854 | cond = false; |
| 1862 | } | 1855 | } else |
| 1856 | iter->oom_lock = true; | ||
| 1863 | } | 1857 | } |
| 1864 | 1858 | ||
| 1865 | if (!failed) | 1859 | if (!failed) |
| 1866 | goto done; | 1860 | return true; |
| 1867 | 1861 | ||
| 1868 | /* | 1862 | /* |
| 1869 | * OK, we failed to lock the whole subtree so we have to clean up | 1863 | * OK, we failed to lock the whole subtree so we have to clean up |
| @@ -1877,8 +1871,7 @@ static bool mem_cgroup_oom_lock(struct mem_cgroup *mem) · 7 unmodified lines | |||
| 1877 | } | 1871 | } |
| 1878 | iter->oom_lock = false; | 1872 | iter->oom_lock = false; |
| 1879 | } | 1873 | } |
| 1880 | done: | 1874 | return false; |
| 1881 | return lock_count; | ||
| 1882 | } | 1875 | } |
| 1883 | 1876 | ||
| 1884 | /* | 1877 | /* |