fscache, cachefiles: Store the volume coherency data

Store the volume coherency data in an xattr and check it when we rebind the
volume.  If it doesn't match the cache volume is moved to the graveyard and
rebuilt anew.

Changes
=======
ver #4:
 - Remove a couple of debugging prints.
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/163967164397.1823006.2950539849831291830.stgit@warthog.procyon.org.uk/ # v3
Link: https://lore.kernel.org/r/164021563138.640689.15851092065380543119.stgit@warthog.procyon.org.uk/ # v4

fs/cachefiles/internal.h

@@ -270,6 +270,8 @@ extern int cachefiles_remove_object_xattr(struct cachefiles_cache *cache,
 					  struct cachefiles_object *object,
 					  struct dentry *dentry);
 extern void cachefiles_prepare_to_write(struct fscache_cookie *cookie);
+extern bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume);
+extern int cachefiles_check_volume_xattr(struct cachefiles_volume *volume);
 
 /*
  * Error handling

fs/cachefiles/volume.c

@@ -22,7 +22,8 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 	struct dentry *vdentry, *fan;
 	size_t len;
 	char *name;
-	int n_accesses, i;
+	bool is_new = false;
+	int ret, n_accesses, i;
 
 	_enter("");
 
@@ -43,11 +44,29 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 	memcpy(name + 1, vcookie->key + 1, len);
 	name[len + 1] = 0;
 
-	vdentry = cachefiles_get_directory(cache, cache->store, name, NULL);
+retry:
+	vdentry = cachefiles_get_directory(cache, cache->store, name, &is_new);
 	if (IS_ERR(vdentry))
 		goto error_name;
 	volume->dentry = vdentry;
 
+	if (is_new) {
+		if (!cachefiles_set_volume_xattr(volume))
+			goto error_dir;
+	} else {
+		ret = cachefiles_check_volume_xattr(volume);
+		if (ret < 0) {
+			if (ret != -ESTALE)
+				goto error_dir;
+			inode_lock_nested(d_inode(cache->store), I_MUTEX_PARENT);
+			cachefiles_bury_object(cache, NULL, cache->store, vdentry,
+					       FSCACHE_VOLUME_IS_WEIRD);
+			cachefiles_put_directory(volume->dentry);
+			cond_resched();
+			goto retry;
+		}
+	}
+	
 	for (i = 0; i < 256; i++) {
 		sprintf(name, "@%02x", i);
 		fan = cachefiles_get_directory(cache, vdentry, name, NULL);
@@ -74,6 +93,7 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
 error_fan:
 	for (i = 0; i < 256; i++)
 		cachefiles_put_directory(volume->fanout[i]);
+error_dir:
 	cachefiles_put_directory(volume->dentry);
 error_name:
 	kfree(name);
@@ -114,5 +134,6 @@ void cachefiles_free_volume(struct fscache_volume *vcookie)
 void cachefiles_withdraw_volume(struct cachefiles_volume *volume)
 {
 	fscache_withdraw_volume(volume->vcookie);
+	cachefiles_set_volume_xattr(volume);
 	__cachefiles_free_volume(volume);
 }

fs/cachefiles/xattr.c

@@ -179,3 +179,81 @@ void cachefiles_prepare_to_write(struct fscache_cookie *cookie)
 		cachefiles_end_secure(cache, saved_cred);
 	}
 }
+
+/*
+ * Set the state xattr on a volume directory.
+ */
+bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume)
+{
+	unsigned int len = volume->vcookie->coherency_len;
+	const void *p = volume->vcookie->coherency;
+	struct dentry *dentry = volume->dentry;
+	int ret;
+
+	_enter("%x,#%d", volume->vcookie->debug_id, len);
+
+	ret = cachefiles_inject_write_error();
+	if (ret == 0)
+		ret = vfs_setxattr(&init_user_ns, dentry, cachefiles_xattr_cache,
+				   p, len, 0);
+	if (ret < 0) {
+		trace_cachefiles_vfs_error(NULL, d_inode(dentry), ret,
+					   cachefiles_trace_setxattr_error);
+		trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino,
+					       cachefiles_coherency_vol_set_fail);
+		if (ret != -ENOMEM)
+			cachefiles_io_error(
+				volume->cache, "Failed to set xattr with error %d", ret);
+	} else {
+		trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino,
+					       cachefiles_coherency_vol_set_ok);
+	}
+
+	_leave(" = %d", ret);
+	return ret == 0;
+}
+
+/*
+ * Check the consistency between the backing cache and the volume cookie.
+ */
+int cachefiles_check_volume_xattr(struct cachefiles_volume *volume)
+{
+	struct cachefiles_xattr *buf;
+	struct dentry *dentry = volume->dentry;
+	unsigned int len = volume->vcookie->coherency_len;
+	const void *p = volume->vcookie->coherency;
+	enum cachefiles_coherency_trace why;
+	ssize_t xlen;
+	int ret = -ESTALE;
+
+	_enter("");
+
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	xlen = cachefiles_inject_read_error();
+	if (xlen == 0)
+		xlen = vfs_getxattr(&init_user_ns, dentry, cachefiles_xattr_cache, buf, len);
+	if (xlen != len) {
+		if (xlen < 0) {
+			trace_cachefiles_vfs_error(NULL, d_inode(dentry), xlen,
+						   cachefiles_trace_getxattr_error);
+			if (xlen == -EIO)
+				cachefiles_io_error(
+					volume->cache,
+					"Failed to read xattr with error %zd", xlen);
+		}
+		why = cachefiles_coherency_vol_check_xattr;
+	} else if (memcmp(buf->data, p, len) != 0) {
+		why = cachefiles_coherency_vol_check_cmp;
+	} else {
+		why = cachefiles_coherency_vol_check_ok;
+		ret = 0;
+	}
+
+	trace_cachefiles_vol_coherency(volume, d_inode(dentry)->i_ino, why);
+	kfree(buf);
+	_leave(" = %d", ret);
+	return ret;
+}

fs/fscache/volume.c

@@ -205,15 +205,22 @@ static struct fscache_volume *fscache_alloc_volume(const char *volume_key,
 	size_t klen, hlen;
 	char *key;
 
+	if (!coherency_data)
+		coherency_len = 0;
+
 	cache = fscache_lookup_cache(cache_name, false);
 	if (IS_ERR(cache))
 		return NULL;
 
-	volume = kzalloc(sizeof(*volume), GFP_KERNEL);
+	volume = kzalloc(struct_size(volume, coherency, coherency_len),
+			 GFP_KERNEL);
 	if (!volume)
 		goto err_cache;
 
 	volume->cache = cache;
+	volume->coherency_len = coherency_len;
+	if (coherency_data)
+		memcpy(volume->coherency, coherency_data, coherency_len);
 	INIT_LIST_HEAD(&volume->proc_link);
 	INIT_WORK(&volume->work, fscache_create_volume_work);
 	refcount_set(&volume->ref, 1);
@@ -421,8 +428,11 @@ void __fscache_relinquish_volume(struct fscache_volume *volume,
 	if (WARN_ON(test_and_set_bit(FSCACHE_VOLUME_RELINQUISHED, &volume->flags)))
 		return;
 
-	if (invalidate)
+	if (invalidate) {
 		set_bit(FSCACHE_VOLUME_INVALIDATE, &volume->flags);
+	} else if (coherency_data) {
+		memcpy(volume->coherency, coherency_data, volume->coherency_len);
+	}
 
 	fscache_put_volume(volume, fscache_volume_put_relinquish);
 }

include/linux/fscache.h

@@ -87,6 +87,8 @@ struct fscache_volume {
 #define FSCACHE_VOLUME_COLLIDED_WITH	2	/* Volume was collided with */
 #define FSCACHE_VOLUME_ACQUIRE_PENDING	3	/* Volume is waiting to complete acquisition */
 #define FSCACHE_VOLUME_CREATING		4	/* Volume is being created on disk */
+	u8				coherency_len;	/* Length of the coherency data */
+	u8				coherency[];	/* Coherency data */
 };
 
 /*

include/trace/events/cachefiles.h

@@ -40,6 +40,7 @@ enum fscache_why_object_killed {
 	FSCACHE_OBJECT_NO_SPACE,
 	FSCACHE_OBJECT_WAS_RETIRED,
 	FSCACHE_OBJECT_WAS_CULLED,
+	FSCACHE_VOLUME_IS_WEIRD,
 };
 
 enum cachefiles_coherency_trace {
@@ -53,6 +54,11 @@ enum cachefiles_coherency_trace {
 	cachefiles_coherency_check_xattr,
 	cachefiles_coherency_set_fail,
 	cachefiles_coherency_set_ok,
+	cachefiles_coherency_vol_check_cmp,
+	cachefiles_coherency_vol_check_ok,
+	cachefiles_coherency_vol_check_xattr,
+	cachefiles_coherency_vol_set_fail,
+	cachefiles_coherency_vol_set_ok,
 };
 
 enum cachefiles_trunc_trace {
@@ -103,7 +109,8 @@ enum cachefiles_error_trace {
 	EM(FSCACHE_OBJECT_INVALIDATED,	"inval")		\
 	EM(FSCACHE_OBJECT_NO_SPACE,	"no_space")		\
 	EM(FSCACHE_OBJECT_WAS_RETIRED,	"was_retired")		\
-	E_(FSCACHE_OBJECT_WAS_CULLED,	"was_culled")
+	EM(FSCACHE_OBJECT_WAS_CULLED,	"was_culled")		\
+	E_(FSCACHE_VOLUME_IS_WEIRD,	"volume_weird")
 
 #define cachefiles_obj_ref_traces					\
 	EM(cachefiles_obj_get_ioreq,		"GET ioreq")		\
@@ -129,7 +136,12 @@ enum cachefiles_error_trace {
 	EM(cachefiles_coherency_check_type,	"BAD type")		\
 	EM(cachefiles_coherency_check_xattr,	"BAD xatt")		\
 	EM(cachefiles_coherency_set_fail,	"SET fail")		\
-	E_(cachefiles_coherency_set_ok,		"SET ok  ")
+	EM(cachefiles_coherency_set_ok,		"SET ok  ")		\
+	EM(cachefiles_coherency_vol_check_cmp,	"VOL BAD cmp ")		\
+	EM(cachefiles_coherency_vol_check_ok,	"VOL OK      ")		\
+	EM(cachefiles_coherency_vol_check_xattr,"VOL BAD xatt")		\
+	EM(cachefiles_coherency_vol_set_fail,	"VOL SET fail")		\
+	E_(cachefiles_coherency_vol_set_ok,	"VOL SET ok  ")
 
 #define cachefiles_trunc_traces						\
 	EM(cachefiles_trunc_dio_adjust,		"DIOADJ")		\
@@ -365,6 +377,32 @@ TRACE_EVENT(cachefiles_coherency,
 		      __entry->content)
 	    );
 
+TRACE_EVENT(cachefiles_vol_coherency,
+	    TP_PROTO(struct cachefiles_volume *volume,
+		     ino_t ino,
+		     enum cachefiles_coherency_trace why),
+
+	    TP_ARGS(volume, ino, why),
+
+	    /* Note that obj may be NULL */
+	    TP_STRUCT__entry(
+		    __field(unsigned int,			vol	)
+		    __field(enum cachefiles_coherency_trace,	why	)
+		    __field(u64,				ino	)
+			     ),
+
+	    TP_fast_assign(
+		    __entry->vol	= volume->vcookie->debug_id;
+		    __entry->why	= why;
+		    __entry->ino	= ino;
+			   ),
+
+	    TP_printk("V=%08x %s i=%llx",
+		      __entry->vol,
+		      __print_symbolic(__entry->why, cachefiles_coherency_traces),
+		      __entry->ino)
+	    );
+
 TRACE_EVENT(cachefiles_prep_read,
 	    TP_PROTO(struct netfs_read_subrequest *sreq,
 		     enum netfs_read_source source,