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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 /fs/cachefiles
parent1800098549fc310cffffefdcb3722adaad0edda8 (diff)
downloadlinux-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 'fs/cachefiles')
-rw-r--r--fs/cachefiles/rdwr.c34
1 files changed, 11 insertions, 23 deletions
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index c994691d944..3367abdcdac 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -176,9 +176,8 @@ static void cachefiles_read_copier(struct fscache_operation *_op)
recheck:
if (PageUptodate(monitor->back_page)) {
copy_highpage(monitor->netfs_page, monitor->back_page);
-
- pagevec_add(&pagevec, monitor->netfs_page);
- fscache_mark_pages_cached(monitor->op, &pagevec);
+ fscache_mark_page_cached(monitor->op,
+ monitor->netfs_page);
error = 0;
} else if (!PageError(monitor->back_page)) {
/* the page has probably been truncated */
@@ -335,8 +334,7 @@ backing_page_already_present:
backing_page_already_uptodate:
_debug("- uptodate");
- pagevec_add(pagevec, netpage);
- fscache_mark_pages_cached(op, pagevec);
+ fscache_mark_page_cached(op, netpage);
copy_highpage(netpage, backpage);
fscache_end_io(op, netpage, 0);
@@ -448,8 +446,7 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
&pagevec);
} else if (cachefiles_has_space(cache, 0, 1) == 0) {
/* there's space in the cache we can use */
- pagevec_add(&pagevec, page);
- fscache_mark_pages_cached(op, &pagevec);
+ fscache_mark_page_cached(op, page);
ret = -ENODATA;
} else {
ret = -ENOBUFS;
@@ -465,8 +462,7 @@ int cachefiles_read_or_alloc_page(struct fscache_retrieval *op,
*/
static int cachefiles_read_backing_file(struct cachefiles_object *object,
struct fscache_retrieval *op,
- struct list_head *list,
- struct pagevec *mark_pvec)
+ struct list_head *list)
{
struct cachefiles_one_read *monitor = NULL;
struct address_space *bmapping = object->backer->d_inode->i_mapping;
@@ -626,13 +622,13 @@ static int cachefiles_read_backing_file(struct cachefiles_object *object,
page_cache_release(backpage);
backpage = NULL;
- if (!pagevec_add(mark_pvec, netpage))
- fscache_mark_pages_cached(op, mark_pvec);
+ fscache_mark_page_cached(op, netpage);
page_cache_get(netpage);
if (!pagevec_add(&lru_pvec, netpage))
__pagevec_lru_add_file(&lru_pvec);
+ /* the netpage is unlocked and marked up to date here */
fscache_end_io(op, netpage, 0);
page_cache_release(netpage);
netpage = NULL;
@@ -775,15 +771,11 @@ int cachefiles_read_or_alloc_pages(struct fscache_retrieval *op,
/* submit the apparently valid pages to the backing fs to be read from
* disk */
if (nrbackpages > 0) {
- ret2 = cachefiles_read_backing_file(object, op, &backpages,
- &pagevec);
+ ret2 = cachefiles_read_backing_file(object, op, &backpages);
if (ret2 == -ENOMEM || ret2 == -EINTR)
ret = ret2;
}
- if (pagevec_count(&pagevec) > 0)
- fscache_mark_pages_cached(op, &pagevec);
-
_leave(" = %d [nr=%u%s]",
ret, *nr_pages, list_empty(pages) ? " empty" : "");
return ret;
@@ -806,7 +798,6 @@ int cachefiles_allocate_page(struct fscache_retrieval *op,
{
struct cachefiles_object *object;
struct cachefiles_cache *cache;
- struct pagevec pagevec;
int ret;
object = container_of(op->op.object,
@@ -817,13 +808,10 @@ int cachefiles_allocate_page(struct fscache_retrieval *op,
_enter("%p,{%lx},", object, page->index);
ret = cachefiles_has_space(cache, 0, 1);
- if (ret == 0) {
- pagevec_init(&pagevec, 0);
- pagevec_add(&pagevec, page);
- fscache_mark_pages_cached(op, &pagevec);
- } else {
+ if (ret == 0)
+ fscache_mark_page_cached(op, page);
+ else
ret = -ENOBUFS;
- }
_leave(" = %d", ret);
return ret;