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authorDavid Howells <dhowells@redhat.com>2012-12-20 21:52:32 +0000
committerDavid Howells <dhowells@redhat.com>2012-12-20 21:54:30 +0000
commitc4d6d8dbf335c7fa47341654a37c53a512b519bb (patch)
tree14f0b9c7146a39aa3770c26bc7c480cf0d2c4f56 /include
parent1800098549fc310cffffefdcb3722adaad0edda8 (diff)
downloadvexpress-lsk-c4d6d8dbf335c7fa47341654a37c53a512b519bb.tar.gz
CacheFiles: Fix the marking of cached pages
Under some circumstances CacheFiles defers the marking of pages with PG_fscache so that it can take advantage of pagevecs to reduce the number of calls to fscache_mark_pages_cached() and the netfs's hook to keep track of this. There are, however, two problems with this: (1) It can lead to the PG_fscache mark being applied _after_ the page is set PG_uptodate and unlocked (by the call to fscache_end_io()). (2) CacheFiles's ref on the page is dropped immediately following fscache_end_io() - and so may not still be held when the mark is applied. This can lead to the page being passed back to the allocator before the mark is applied. Fix this by, where appropriate, marking the page before calling fscache_end_io() and releasing the page. This means that we can't take advantage of pagevecs and have to make a separate call for each page to the marking routines. The symptoms of this are Bad Page state errors cropping up under memory pressure, for example: BUG: Bad page state in process tar pfn:002da page:ffffea0000009fb0 count:0 mapcount:0 mapping: (null) index:0x1447 page flags: 0x1000(private_2) Pid: 4574, comm: tar Tainted: G W 3.1.0-rc4-fsdevel+ #1064 Call Trace: [<ffffffff8109583c>] ? dump_page+0xb9/0xbe [<ffffffff81095916>] bad_page+0xd5/0xea [<ffffffff81095d82>] get_page_from_freelist+0x35b/0x46a [<ffffffff810961f3>] __alloc_pages_nodemask+0x362/0x662 [<ffffffff810989da>] __do_page_cache_readahead+0x13a/0x267 [<ffffffff81098942>] ? __do_page_cache_readahead+0xa2/0x267 [<ffffffff81098d7b>] ra_submit+0x1c/0x20 [<ffffffff8109900a>] ondemand_readahead+0x28b/0x29a [<ffffffff81098ee2>] ? ondemand_readahead+0x163/0x29a [<ffffffff810990ce>] page_cache_sync_readahead+0x38/0x3a [<ffffffff81091d8a>] generic_file_aio_read+0x2ab/0x67e [<ffffffffa008cfbe>] nfs_file_read+0xa4/0xc9 [nfs] [<ffffffff810c22c4>] do_sync_read+0xba/0xfa [<ffffffff81177a47>] ? security_file_permission+0x7b/0x84 [<ffffffff810c25dd>] ? rw_verify_area+0xab/0xc8 [<ffffffff810c29a4>] vfs_read+0xaa/0x13a [<ffffffff810c2a79>] sys_read+0x45/0x6c [<ffffffff813ac37b>] system_call_fastpath+0x16/0x1b As can be seen, PG_private_2 (== PG_fscache) is set in the page flags. Instrumenting fscache_mark_pages_cached() to verify whether page->mapping was set appropriately showed that sometimes it wasn't. This led to the discovery that sometimes the page has apparently been reclaimed by the time the marker got to see it. Reported-by: M. Stevens <m@tippett.com> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Jeff Layton <jlayton@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/fscache-cache.h3
-rw-r--r--include/linux/fscache.h12
2 files changed, 9 insertions, 6 deletions
diff --git a/include/linux/fscache-cache.h b/include/linux/fscache-cache.h
index ce31408b1e4..9879183b55d 100644
--- a/include/linux/fscache-cache.h
+++ b/include/linux/fscache-cache.h
@@ -504,6 +504,9 @@ extern void fscache_withdraw_cache(struct fscache_cache *cache);
extern void fscache_io_error(struct fscache_cache *cache);
+extern void fscache_mark_page_cached(struct fscache_retrieval *op,
+ struct page *page);
+
extern void fscache_mark_pages_cached(struct fscache_retrieval *op,
struct pagevec *pagevec);
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 9ec20dec335..f4b6353543b 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -135,14 +135,14 @@ struct fscache_cookie_def {
*/
void (*put_context)(void *cookie_netfs_data, void *context);
- /* indicate pages that now have cache metadata retained
- * - this function should mark the specified pages as now being cached
- * - the pages will have been marked with PG_fscache before this is
+ /* indicate page that now have cache metadata retained
+ * - this function should mark the specified page as now being cached
+ * - the page will have been marked with PG_fscache before this is
* called, so this is optional
*/
- void (*mark_pages_cached)(void *cookie_netfs_data,
- struct address_space *mapping,
- struct pagevec *cached_pvec);
+ void (*mark_page_cached)(void *cookie_netfs_data,
+ struct address_space *mapping,
+ struct page *page);
/* indicate the cookie is no longer cached
* - this function is called when the backing store currently caching