On Sun, 3 Oct 2010 23:57:59 -0700
Greg Thelen <gthelen@xxxxxxxxxx> wrote:
> If pages are being migrated from a memcg, then updates to that
> memcg's page statistics are protected by grabbing a bit spin lock
> using lock_page_cgroup(). In an upcoming commit memcg dirty page
> accounting will be updating memcg page accounting (specifically:
> num writeback pages) from softirq. Avoid a deadlocking nested
> spin lock attempt by disabling interrupts on the local processor
> when grabbing the page_cgroup bit_spin_lock in lock_page_cgroup().
> This avoids the following deadlock:
> statistic
> CPU 0 CPU 1
> inc_file_mapped
> rcu_read_lock
> start move
> synchronize_rcu
> lock_page_cgroup
> softirq
> test_clear_page_writeback
> mem_cgroup_dec_page_stat(NR_WRITEBACK)
> rcu_read_lock
> lock_page_cgroup /* deadlock */
> unlock_page_cgroup
> rcu_read_unlock
> unlock_page_cgroup
> rcu_read_unlock
>
> By disabling interrupts in lock_page_cgroup, nested calls
> are avoided. The softirq would be delayed until after inc_file_mapped
> enables interrupts when calling unlock_page_cgroup().
>
> The normal, fast path, of memcg page stat updates typically
> does not need to call lock_page_cgroup(), so this change does
> not affect the performance of the common case page accounting.
>
> Signed-off-by: Andrea Righi <arighi@xxxxxxxxxxx>
> Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx>
Nice Catch!
But..hmm this wasn't necessary for FILE_MAPPED but necesary for new
statistics, right ? (This affects the order of patches.)
Anyway
Acked-By: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> ---
> include/linux/page_cgroup.h | 8 +++++-
> mm/memcontrol.c | 51 +++++++++++++++++++++++++-----------------
> 2 files changed, 36 insertions(+), 23 deletions(-)
>
> diff --git a/include/linux/page_cgroup.h b/include/linux/page_cgroup.h
> index b59c298..872f6b1 100644
> --- a/include/linux/page_cgroup.h
> +++ b/include/linux/page_cgroup.h
> @@ -117,14 +117,18 @@ static inline enum zone_type page_cgroup_zid(struct page_cgroup *pc)
> return page_zonenum(pc->page);
> }
>
> -static inline void lock_page_cgroup(struct page_cgroup *pc)
> +static inline void lock_page_cgroup(struct page_cgroup *pc,
> + unsigned long *flags)
> {
> + local_irq_save(*flags);
> bit_spin_lock(PCG_LOCK, &pc->flags);
> }
>
> -static inline void unlock_page_cgroup(struct page_cgroup *pc)
> +static inline void unlock_page_cgroup(struct page_cgroup *pc,
> + unsigned long flags)
> {
> bit_spin_unlock(PCG_LOCK, &pc->flags);
> + local_irq_restore(flags);
> }
>
> #else /* CONFIG_CGROUP_MEM_RES_CTLR */
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f4259f4..267d774 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1599,6 +1599,7 @@ void mem_cgroup_update_page_stat(struct page *page,
> struct mem_cgroup *mem;
> struct page_cgroup *pc = lookup_page_cgroup(page);
> bool need_unlock = false;
> + unsigned long flags;
>
> if (unlikely(!pc))
> return;
> @@ -1610,7 +1611,7 @@ void mem_cgroup_update_page_stat(struct page *page,
> /* pc->mem_cgroup is unstable ? */
> if (unlikely(mem_cgroup_stealed(mem))) {
> /* take a lock against to access pc->mem_cgroup */
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> need_unlock = true;
> mem = pc->mem_cgroup;
> if (!mem || !PageCgroupUsed(pc))
> @@ -1633,7 +1634,7 @@ void mem_cgroup_update_page_stat(struct page *page,
>
> out:
> if (unlikely(need_unlock))
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> rcu_read_unlock();
> return;
> }
> @@ -2053,11 +2054,12 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> struct page_cgroup *pc;
> unsigned short id;
> swp_entry_t ent;
> + unsigned long flags;
>
> VM_BUG_ON(!PageLocked(page));
>
> pc = lookup_page_cgroup(page);
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> if (PageCgroupUsed(pc)) {
> mem = pc->mem_cgroup;
> if (mem && !css_tryget(&mem->css))
> @@ -2071,7 +2073,7 @@ struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
> mem = NULL;
> rcu_read_unlock();
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return mem;
> }
>
> @@ -2084,13 +2086,15 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
> struct page_cgroup *pc,
> enum charge_type ctype)
> {
> + unsigned long flags;
> +
> /* try_charge() can return NULL to *memcg, taking care of it. */
> if (!mem)
> return;
>
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> if (unlikely(PageCgroupUsed(pc))) {
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> mem_cgroup_cancel_charge(mem);
> return;
> }
> @@ -2120,7 +2124,7 @@ static void __mem_cgroup_commit_charge(struct mem_cgroup *mem,
>
> mem_cgroup_charge_statistics(mem, pc, true);
>
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * "charge_statistics" updated event counter. Then, check it.
> * Insert ancestor (and ancestor's ancestors), to softlimit RB-tree.
> @@ -2187,12 +2191,13 @@ static int mem_cgroup_move_account(struct page_cgroup *pc,
> struct mem_cgroup *from, struct mem_cgroup *to, bool uncharge)
> {
> int ret = -EINVAL;
> - lock_page_cgroup(pc);
> + unsigned long flags;
> + lock_page_cgroup(pc, &flags);
> if (PageCgroupUsed(pc) && pc->mem_cgroup == from) {
> __mem_cgroup_move_account(pc, from, to, uncharge);
> ret = 0;
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * check events
> */
> @@ -2298,6 +2303,7 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> gfp_t gfp_mask)
> {
> int ret;
> + unsigned long flags;
>
> if (mem_cgroup_disabled())
> return 0;
> @@ -2320,12 +2326,12 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
> pc = lookup_page_cgroup(page);
> if (!pc)
> return 0;
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> if (PageCgroupUsed(pc)) {
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return 0;
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> }
>
> if (unlikely(!mm))
> @@ -2511,6 +2517,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> {
> struct page_cgroup *pc;
> struct mem_cgroup *mem = NULL;
> + unsigned long flags;
>
> if (mem_cgroup_disabled())
> return NULL;
> @@ -2525,7 +2532,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> if (unlikely(!pc || !PageCgroupUsed(pc)))
> return NULL;
>
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
>
> mem = pc->mem_cgroup;
>
> @@ -2560,7 +2567,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> * special functions.
> */
>
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * even after unlock, we have mem->res.usage here and this memcg
> * will never be freed.
> @@ -2576,7 +2583,7 @@ __mem_cgroup_uncharge_common(struct page *page, enum charge_type ctype)
> return mem;
>
> unlock_out:
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> return NULL;
> }
>
> @@ -2765,12 +2772,13 @@ int mem_cgroup_prepare_migration(struct page *page,
> struct mem_cgroup *mem = NULL;
> enum charge_type ctype;
> int ret = 0;
> + unsigned long flags;
>
> if (mem_cgroup_disabled())
> return 0;
>
> pc = lookup_page_cgroup(page);
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> if (PageCgroupUsed(pc)) {
> mem = pc->mem_cgroup;
> css_get(&mem->css);
> @@ -2806,7 +2814,7 @@ int mem_cgroup_prepare_migration(struct page *page,
> if (PageAnon(page))
> SetPageCgroupMigration(pc);
> }
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * If the page is not charged at this point,
> * we return here.
> @@ -2819,9 +2827,9 @@ int mem_cgroup_prepare_migration(struct page *page,
> css_put(&mem->css);/* drop extra refcnt */
> if (ret || *ptr == NULL) {
> if (PageAnon(page)) {
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> ClearPageCgroupMigration(pc);
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
> /*
> * The old page may be fully unmapped while we kept it.
> */
> @@ -2852,6 +2860,7 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
> {
> struct page *used, *unused;
> struct page_cgroup *pc;
> + unsigned long flags;
>
> if (!mem)
> return;
> @@ -2871,9 +2880,9 @@ void mem_cgroup_end_migration(struct mem_cgroup *mem,
> * Clear the flag and check the page should be charged.
> */
> pc = lookup_page_cgroup(oldpage);
> - lock_page_cgroup(pc);
> + lock_page_cgroup(pc, &flags);
> ClearPageCgroupMigration(pc);
> - unlock_page_cgroup(pc);
> + unlock_page_cgroup(pc, flags);
>
> __mem_cgroup_uncharge_common(unused, MEM_CGROUP_CHARGE_TYPE_FORCE);
>
> --
> 1.7.1
>
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