Re: [PATCH] mm: memcontrol: fix possible css ref leak on oom
From: Michal Hocko <mhocko@kernel.org>
Date: 2016-05-24 09:22:09
Also in:
lkml
Subsystem:
memory management, page cache, the rest · Maintainers:
Andrew Morton, Matthew Wilcox, Jan Kara, Linus Torvalds
On Tue 24-05-16 12:01:42, Vladimir Davydov wrote:
On Tue, May 24, 2016 at 10:47:37AM +0200, Michal Hocko wrote:quoted
On Tue 24-05-16 11:43:19, Vladimir Davydov wrote:quoted
On Mon, May 23, 2016 at 07:44:43PM +0200, Michal Hocko wrote:quoted
On Mon 23-05-16 19:02:10, Vladimir Davydov wrote:quoted
mem_cgroup_oom may be invoked multiple times while a process is handling a page fault, in which case current->memcg_in_oom will be overwritten leaking the previously taken css reference.Have you seen this happening? I was under impression that the page fault paths that have oom enabled will not retry allocations.filemap_fault will, for readahead.I thought that the readahead is __GFP_NORETRY so we do not trigger OOM killer.Hmm, interesting. We do allocate readahead pages with __GFP_NORETRY, but we add them to page cache and hence charge with GFP_KERNEL or GFP_NOFS mask, see __do_page_cache_readahaed -> read_pages.
I guess we do not want to trigger OOM just because of readahead. What do you think about the following? I will cook up a full patch if this (untested) looks ok. ---
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 97354102794d..81363b834900 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h@@ -209,10 +209,10 @@ static inline struct page *page_cache_alloc_cold(struct address_space *x) return __page_cache_alloc(mapping_gfp_mask(x)|__GFP_COLD); } -static inline struct page *page_cache_alloc_readahead(struct address_space *x) +static inline gfp_t readahead_gfp_mask(struct address_space *x) { - return __page_cache_alloc(mapping_gfp_mask(x) | - __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN); + return mapping_gfp_mask(x) | + __GFP_COLD | __GFP_NORETRY | __GFP_NOWARN; } typedef int filler_t(void *, struct page *);
diff --git a/mm/readahead.c b/mm/readahead.c
index 40be3ae0afe3..7431fefe4ede 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c@@ -108,7 +108,7 @@ int read_cache_pages(struct address_space *mapping, struct list_head *pages, EXPORT_SYMBOL(read_cache_pages); static int read_pages(struct address_space *mapping, struct file *filp, - struct list_head *pages, unsigned nr_pages) + struct list_head *pages, unsigned nr_pages, gfp_t gfp_mask) { struct blk_plug plug; unsigned page_idx;
@@ -126,8 +126,7 @@ static int read_pages(struct address_space *mapping, struct file *filp, for (page_idx = 0; page_idx < nr_pages; page_idx++) { struct page *page = lru_to_page(pages); list_del(&page->lru); - if (!add_to_page_cache_lru(page, mapping, page->index, - mapping_gfp_constraint(mapping, GFP_KERNEL))) { + if (!add_to_page_cache_lru(page, mapping, page->index, gfp_mask)) { mapping->a_ops->readpage(filp, page); } put_page(page);
@@ -159,6 +158,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, int page_idx; int ret = 0; loff_t isize = i_size_read(inode); + gfp_t gfp_mask = readahead_gfp_mask(mapping); if (isize == 0) goto out;
@@ -180,7 +180,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, if (page && !radix_tree_exceptional_entry(page)) continue; - page = page_cache_alloc_readahead(mapping); + page = __page_cache_alloc(gfp_mask); if (!page) break; page->index = page_offset;
@@ -196,7 +196,7 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, * will then handle the error. */ if (ret) - read_pages(mapping, filp, &page_pool, ret); + read_pages(mapping, filp, &page_pool, ret, gfp_mask); BUG_ON(!list_empty(&page_pool)); out: return ret;
--
Michal Hocko
SUSE Labs
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