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authorMichal Hocko <mhocko@suse.cz>2011-08-09 11:56:26 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2011-08-09 17:04:43 -0700
commit9f50fad65b87a8776ae989ca059ad6c17925dfc3 (patch)
tree9d15fc968323357da6b3a534c4c40ff3192cf2f9 /mm
parent47e180d6523081605c970f806572beab8a205537 (diff)
downloadlinux-linaro-precise-9f50fad65b87a8776ae989ca059ad6c17925dfc3.tar.gz
Revert "memcg: get rid of percpu_charge_mutex lock"
This reverts commit 8521fc50d433507a7cdc96bec280f9e5888a54cc. The patch incorrectly assumes that using atomic FLUSHING_CACHED_CHARGE bit operations is sufficient but that is not true. Johannes Weiner has reported a crash during parallel memory cgroup removal: BUG: unable to handle kernel NULL pointer dereference at 0000000000000018 IP: [<ffffffff81083b70>] css_is_ancestor+0x20/0x70 Oops: 0000 [#1] PREEMPT SMP Pid: 19677, comm: rmdir Tainted: G W 3.0.0-mm1-00188-gf38d32b #35 ECS MCP61M-M3/MCP61M-M3 RIP: 0010:[<ffffffff81083b70>] css_is_ancestor+0x20/0x70 RSP: 0018:ffff880077b09c88 EFLAGS: 00010202 Process rmdir (pid: 19677, threadinfo ffff880077b08000, task ffff8800781bb310) Call Trace: [<ffffffff810feba3>] mem_cgroup_same_or_subtree+0x33/0x40 [<ffffffff810feccf>] drain_all_stock+0x11f/0x170 [<ffffffff81103211>] mem_cgroup_force_empty+0x231/0x6d0 [<ffffffff811036c4>] mem_cgroup_pre_destroy+0x14/0x20 [<ffffffff81080559>] cgroup_rmdir+0xb9/0x500 [<ffffffff81114d26>] vfs_rmdir+0x86/0xe0 [<ffffffff81114e7b>] do_rmdir+0xfb/0x110 [<ffffffff81114ea6>] sys_rmdir+0x16/0x20 [<ffffffff8154d76b>] system_call_fastpath+0x16/0x1b We are crashing because we try to dereference cached memcg when we are checking whether we should wait for draining on the cache. The cache is already cleaned up, though. There is also a theoretical chance that the cached memcg gets freed between we test for the FLUSHING_CACHED_CHARGE and dereference it in mem_cgroup_same_or_subtree: CPU0 CPU1 CPU2 mem=stock->cached stock->cached=NULL clear_bit test_and_set_bit test_bit() ... <preempted> mem_cgroup_destroy use after free The percpu_charge_mutex protected from this race because sync draining is exclusive. It is safer to revert now and come up with a more parallel implementation later. Signed-off-by: Michal Hocko <mhocko@suse.cz> Reported-by: Johannes Weiner <jweiner@redhat.com> Acked-by: Johannes Weiner <jweiner@redhat.com> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/memcontrol.c12
1 files changed, 10 insertions, 2 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f4ec4e7ca4c..930de943727 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2091,6 +2091,7 @@ struct memcg_stock_pcp {
#define FLUSHING_CACHED_CHARGE (0)
};
static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
+static DEFINE_MUTEX(percpu_charge_mutex);
/*
* Try to consume stocked charge on this cpu. If success, one page is consumed
@@ -2197,8 +2198,7 @@ static void drain_all_stock(struct mem_cgroup *root_mem, bool sync)
for_each_online_cpu(cpu) {
struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
- if (mem_cgroup_same_or_subtree(root_mem, stock->cached) &&
- test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
+ if (test_bit(FLUSHING_CACHED_CHARGE, &stock->flags))
flush_work(&stock->work);
}
out:
@@ -2213,14 +2213,22 @@ out:
*/
static void drain_all_stock_async(struct mem_cgroup *root_mem)
{
+ /*
+ * If someone calls draining, avoid adding more kworker runs.
+ */
+ if (!mutex_trylock(&percpu_charge_mutex))
+ return;
drain_all_stock(root_mem, false);
+ mutex_unlock(&percpu_charge_mutex);
}
/* This is a synchronous drain interface. */
static void drain_all_stock_sync(struct mem_cgroup *root_mem)
{
/* called when force_empty is called */
+ mutex_lock(&percpu_charge_mutex);
drain_all_stock(root_mem, true);
+ mutex_unlock(&percpu_charge_mutex);
}
/*