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memcg: correctly order reading PCG_USED and pc->mem_cgroup
The placement of the read-side barrier is confused: the writer first sets pc->mem_cgroup, then PCG_USED. The read-side barrier has to be between testing PCG_USED and reading pc->mem_cgroup. Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> Cc: Balbir Singh <balbir@linux.vnet.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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2550326ac7
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1 changed files with 9 additions and 18 deletions
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@ -836,13 +836,12 @@ void mem_cgroup_rotate_lru_list(struct page *page, enum lru_list lru)
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return;
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return;
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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/*
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* Used bit is set without atomic ops but after smp_wmb().
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* For making pc->mem_cgroup visible, insert smp_rmb() here.
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*/
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smp_rmb();
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/* unused or root page is not rotated. */
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/* unused or root page is not rotated. */
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if (!PageCgroupUsed(pc) || mem_cgroup_is_root(pc->mem_cgroup))
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if (!PageCgroupUsed(pc))
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return;
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/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
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smp_rmb();
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if (mem_cgroup_is_root(pc->mem_cgroup))
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return;
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return;
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mz = page_cgroup_zoneinfo(pc);
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mz = page_cgroup_zoneinfo(pc);
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list_move(&pc->lru, &mz->lists[lru]);
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list_move(&pc->lru, &mz->lists[lru]);
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@ -857,14 +856,10 @@ void mem_cgroup_add_lru_list(struct page *page, enum lru_list lru)
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return;
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return;
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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VM_BUG_ON(PageCgroupAcctLRU(pc));
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VM_BUG_ON(PageCgroupAcctLRU(pc));
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/*
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* Used bit is set without atomic ops but after smp_wmb().
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* For making pc->mem_cgroup visible, insert smp_rmb() here.
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*/
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smp_rmb();
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if (!PageCgroupUsed(pc))
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if (!PageCgroupUsed(pc))
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return;
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return;
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/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
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smp_rmb();
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mz = page_cgroup_zoneinfo(pc);
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mz = page_cgroup_zoneinfo(pc);
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/* huge page split is done under lru_lock. so, we have no races. */
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/* huge page split is done under lru_lock. so, we have no races. */
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MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
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MEM_CGROUP_ZSTAT(mz, lru) += 1 << compound_order(page);
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@ -1031,14 +1026,10 @@ mem_cgroup_get_reclaim_stat_from_page(struct page *page)
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return NULL;
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return NULL;
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pc = lookup_page_cgroup(page);
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pc = lookup_page_cgroup(page);
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/*
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* Used bit is set without atomic ops but after smp_wmb().
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* For making pc->mem_cgroup visible, insert smp_rmb() here.
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*/
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smp_rmb();
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if (!PageCgroupUsed(pc))
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if (!PageCgroupUsed(pc))
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return NULL;
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return NULL;
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/* Ensure pc->mem_cgroup is visible after reading PCG_USED. */
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smp_rmb();
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mz = page_cgroup_zoneinfo(pc);
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mz = page_cgroup_zoneinfo(pc);
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if (!mz)
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if (!mz)
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return NULL;
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return NULL;
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