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Subject[PATCH] FS-Cache: Fix handling of an attempt to store a page that is now beyond EOF
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Fix the handling of an attempt to store a page that is now beyond EOF.  This
may happen, for example, if the page got pushed for storage before the netfs
file got truncated on the server. In such a case, we should just remove the
excessive pages from the cookie->stores radix tree and wake up the waiter.

This can be seen in /proc/fs/fscache/stats on this line:

Stores : ops=350 run=1895 pgs=1545 rxd=1727 olm=9

where olm=N has N > 0.

Reported-by: Milosz Tanski <milosz@adfin.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Milosz Tanski <milosz@adfin.com>
---

fs/fscache/page.c | 37 ++++++++++++++++++++++++++++++++++++-
1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/fs/fscache/page.c b/fs/fscache/page.c
index 7f5c658af755..b4730cf52aec 100644
--- a/fs/fscache/page.c
+++ b/fs/fscache/page.c
@@ -755,6 +755,7 @@ static void fscache_write_op(struct fscache_operation *_op)
struct fscache_object *object = op->op.object;
struct fscache_cookie *cookie;
struct page *page;
+ pgoff_t index;
unsigned n;
void *results[1];
int ret;
@@ -803,7 +804,7 @@ static void fscache_write_op(struct fscache_operation *_op)
_debug("gang %d [%lx]", n, page->index);
if (page->index > op->store_limit) {
fscache_stat(&fscache_n_store_pages_over_limit);
- goto superseded;
+ goto page_beyond_limit;
}

radix_tree_tag_set(&cookie->stores, page->index,
@@ -829,6 +830,40 @@ static void fscache_write_op(struct fscache_operation *_op)
_leave("");
return;

+page_beyond_limit:
+ spin_unlock(&object->lock);
+
+page_beyond_limit_unlocked:
+ /* pages that are now beyond the end of the storage object must have
+ * their pending storage records cleared.
+ */
+ index = page->index;
+ radix_tree_tag_clear(&cookie->stores, page->index,
+ FSCACHE_COOKIE_PENDING_TAG);
+ if (!radix_tree_tag_get(&cookie->stores, page->index,
+ FSCACHE_COOKIE_STORING_TAG)) {
+ fscache_stat(&fscache_n_store_radix_deletes);
+ radix_tree_delete(&cookie->stores, page->index);
+ page_cache_release(page);
+ }
+ if (!need_resched()) {
+ n = radix_tree_gang_lookup_tag(&cookie->stores, results,
+ index + 1, 1,
+ FSCACHE_COOKIE_PENDING_TAG);
+ if (n == 1) {
+ page = results[0];
+ goto page_beyond_limit_unlocked;
+ }
+ spin_unlock(&cookie->stores_lock);
+ wake_up_bit(&cookie->flags, 0);
+ } else {
+ spin_unlock(&cookie->stores_lock);
+ }
+
+ fscache_enqueue_operation(&op->op);
+ _leave("");
+ return;
+
superseded:
/* this writer is going away and there aren't any more things to
* write */


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