FS-Cache: Handle read request vs lookup, creation or other cache failure

FS-Cache doesn't correctly handle the netfs requesting a read from the cache
on an object that failed or was withdrawn by the cache.  A trace similar to
the following might be seen:

	CacheFiles: Lookup failed error -105
	[exe   ] unexpected submission OP165afe [OBJ6cac OBJECT_LC_DYING]
	[exe   ] objstate=OBJECT_LC_DYING [OBJECT_LC_DYING]
	[exe   ] objflags=0
	[exe   ] objevent=9 [fffffffffffffffb]
	[exe   ] ops=0 inp=0 exc=0
	Pid: 6970, comm: exe Not tainted 2.6.32-rc6-cachefs #50
	Call Trace:
	 [<ffffffffa0076477>] fscache_submit_op+0x3ff/0x45a [fscache]
	 [<ffffffffa0077997>] __fscache_read_or_alloc_pages+0x187/0x3c4 [fscache]
	 [<ffffffffa00b6480>] ? nfs_readpage_from_fscache_complete+0x0/0x66 [nfs]
	 [<ffffffffa00b6388>] __nfs_readpages_from_fscache+0x7e/0x176 [nfs]
	 [<ffffffff8108e483>] ? __alloc_pages_nodemask+0x11c/0x5cf
	 [<ffffffffa009d796>] nfs_readpages+0x114/0x1d7 [nfs]
	 [<ffffffff81090314>] __do_page_cache_readahead+0x15f/0x1ec
	 [<ffffffff81090228>] ? __do_page_cache_readahead+0x73/0x1ec
	 [<ffffffff810903bd>] ra_submit+0x1c/0x20
	 [<ffffffff810906bb>] ondemand_readahead+0x227/0x23a
	 [<ffffffff81090762>] page_cache_sync_readahead+0x17/0x19
	 [<ffffffff8108a99e>] generic_file_aio_read+0x236/0x5a0
	 [<ffffffffa00937bd>] nfs_file_read+0xe4/0xf3 [nfs]
	 [<ffffffff810b2fa2>] do_sync_read+0xe3/0x120
	 [<ffffffff81354cc3>] ? _spin_unlock_irq+0x2b/0x31
	 [<ffffffff8104c0f1>] ? autoremove_wake_function+0x0/0x34
	 [<ffffffff811848e5>] ? selinux_file_permission+0x5d/0x10f
	 [<ffffffff81352bdb>] ? thread_return+0x3e/0x101
	 [<ffffffff8117d7b0>] ? security_file_permission+0x11/0x13
	 [<ffffffff810b3b06>] vfs_read+0xaa/0x16f
	 [<ffffffff81058df0>] ? trace_hardirqs_on_caller+0x10c/0x130
	 [<ffffffff810b3c84>] sys_read+0x45/0x6c
	 [<ffffffff8100ae2b>] system_call_fastpath+0x16/0x1b

The object state might also be OBJECT_DYING or OBJECT_WITHDRAWING.

This should be handled by simply rejecting the new operation with ENOBUFS.
There's no need to log an error for it.  Events of this type now appear in the
stats file under Ops:rej.

Signed-off-by: David Howells <dhowells@redhat.com>

diff --git a/Documentation/filesystems/caching/fscache.txt b/Documentation/filesystems/caching/fscache.txt
index 9cf2cfbc81c98f95e211e6982e1ed123d0d5d4ef..057a3c71d524925fe500961ffdd01947d08e5a14 100644 (file)
--- a/Documentation/filesystems/caching/fscache.txt
+++ b/Documentation/filesystems/caching/fscache.txt
@@ -276,6 +276,7 @@ proc files.
                run=N   Number of times async ops given CPU time
                enq=N   Number of times async ops queued for processing
                can=N   Number of async ops cancelled
+               rej=N   Number of async ops rejected due to object lookup/create failure
                dfr=N   Number of async ops queued for deferred release
                rel=N   Number of async ops released
                gc=N    Number of deferred-release async ops garbage collected

diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h
index ba1853fa1ff93934fad9926055fa3326fb92d2cd..a0769872b19cc03da608508716862432e1e262bb 100644 (file)
--- a/fs/fscache/internal.h
+++ b/fs/fscache/internal.h
@@ -143,6 +143,7 @@ extern atomic_t fscache_n_op_deferred_release;
 extern atomic_t fscache_n_op_release;
 extern atomic_t fscache_n_op_gc;
 extern atomic_t fscache_n_op_cancelled;
+extern atomic_t fscache_n_op_rejected;
 
 extern atomic_t fscache_n_attr_changed;
 extern atomic_t fscache_n_attr_changed_ok;

diff --git a/fs/fscache/operation.c b/fs/fscache/operation.c
index 296492efb81b74ede679a326b7ccff4d1b86a29f..313e79a14266e69e2a47aafdffefc89b29f510df 100644 (file)
--- a/fs/fscache/operation.c
+++ b/fs/fscache/operation.c
@@ -232,6 +232,11 @@ int fscache_submit_op(struct fscache_object *object,
                list_add_tail(&op->pend_link, &object->pending_ops);
                fscache_stat(&fscache_n_op_pend);
                ret = 0;
+       } else if (object->state == FSCACHE_OBJECT_DYING ||
+                  object->state == FSCACHE_OBJECT_LC_DYING ||
+                  object->state == FSCACHE_OBJECT_WITHDRAWING) {
+               fscache_stat(&fscache_n_op_rejected);
+               ret = -ENOBUFS;
        } else if (!test_bit(FSCACHE_IOERROR, &object->cache->flags)) {
                fscache_report_unexpected_submission(object, op, ostate);
                ASSERT(!fscache_object_is_active(object));

diff --git a/fs/fscache/stats.c b/fs/fscache/stats.c
index 1d53ea68409e437d29165b8c35c8214a2eedb6aa..045ba396dbf23b4da43b797acbb98e2a0c72c330 100644 (file)
--- a/fs/fscache/stats.c
+++ b/fs/fscache/stats.c
@@ -26,6 +26,7 @@ atomic_t fscache_n_op_deferred_release;
 atomic_t fscache_n_op_release;
 atomic_t fscache_n_op_gc;
 atomic_t fscache_n_op_cancelled;
+atomic_t fscache_n_op_rejected;
 
 atomic_t fscache_n_attr_changed;
 atomic_t fscache_n_attr_changed_ok;
@@ -210,11 +211,12 @@ static int fscache_stats_show(struct seq_file *m, void *v)
                   atomic_read(&fscache_n_store_radix_deletes),
                   atomic_read(&fscache_n_store_pages_over_limit));
 
-       seq_printf(m, "Ops    : pend=%u run=%u enq=%u can=%u\n",
+       seq_printf(m, "Ops    : pend=%u run=%u enq=%u can=%u rej=%u\n",
                   atomic_read(&fscache_n_op_pend),
                   atomic_read(&fscache_n_op_run),
                   atomic_read(&fscache_n_op_enqueue),
-                  atomic_read(&fscache_n_op_cancelled));
+                  atomic_read(&fscache_n_op_cancelled),
+                  atomic_read(&fscache_n_op_rejected));
        seq_printf(m, "Ops    : dfr=%u rel=%u gc=%u\n",
                   atomic_read(&fscache_n_op_deferred_release),
                   atomic_read(&fscache_n_op_release),