When an anonymous fd is closed by user daemon, if there is a new read
request for this file comes up, the anonymous fd should be re-opened
to handle that read request rather than fail it directly.
1. Introduce reopening state for objects that are closed but have
inflight/subsequent read requests.
2. No longer flush READ requests but only CLOSE requests when anonymous
fd is closed.
3. Enqueue the reopen work to workqueue, thus user daemon could get rid
of daemon_read context and handle that request smoothly. Otherwise,
the user daemon will send a reopen request and wait for itself to
process the request.
Signed-off-by: Jia Zhu <[email protected]>
Reviewed-by: Xin Yin <[email protected]>
Reviewed-by: Jingbo Xu <[email protected]>
---
fs/cachefiles/internal.h | 3 ++
fs/cachefiles/ondemand.c | 98 ++++++++++++++++++++++++++++------------
2 files changed, 72 insertions(+), 29 deletions(-)
diff --git a/fs/cachefiles/internal.h b/fs/cachefiles/internal.h
index beaf3a8785ce..2ed836d4169e 100644
--- a/fs/cachefiles/internal.h
+++ b/fs/cachefiles/internal.h
@@ -47,9 +47,11 @@ struct cachefiles_volume {
enum cachefiles_object_state {
CACHEFILES_ONDEMAND_OBJSTATE_close, /* Anonymous fd closed by daemon or initial state */
CACHEFILES_ONDEMAND_OBJSTATE_open, /* Anonymous fd associated with object is available */
+ CACHEFILES_ONDEMAND_OBJSTATE_reopening, /* Object that was closed and is being reopened. */
};
struct cachefiles_ondemand_info {
+ struct work_struct work;
int ondemand_id;
enum cachefiles_object_state state;
struct cachefiles_object *object;
@@ -323,6 +325,7 @@ cachefiles_ondemand_set_object_##_state(struct cachefiles_object *object) \
CACHEFILES_OBJECT_STATE_FUNCS(open);
CACHEFILES_OBJECT_STATE_FUNCS(close);
+CACHEFILES_OBJECT_STATE_FUNCS(reopening);
#else
static inline ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
char __user *_buffer, size_t buflen)
diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 6e47667c6690..8e7f8c152a5b 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -18,14 +18,10 @@ static int cachefiles_ondemand_fd_release(struct inode *inode,
info->ondemand_id = CACHEFILES_ONDEMAND_ID_CLOSED;
cachefiles_ondemand_set_object_close(object);
- /*
- * Flush all pending READ requests since their completion depends on
- * anon_fd.
- */
- xas_for_each(&xas, req, ULONG_MAX) {
+ /* Only flush CACHEFILES_REQ_NEW marked req to avoid race with daemon_read */
+ xas_for_each_marked(&xas, req, ULONG_MAX, CACHEFILES_REQ_NEW) {
if (req->msg.object_id == object_id &&
- req->msg.opcode == CACHEFILES_OP_READ) {
- req->error = -EIO;
+ req->msg.opcode == CACHEFILES_OP_CLOSE) {
complete(&req->done);
xas_store(&xas, NULL);
}
@@ -179,6 +175,7 @@ int cachefiles_ondemand_copen(struct cachefiles_cache *cache, char *args)
trace_cachefiles_ondemand_copen(req->object, id, size);
cachefiles_ondemand_set_object_open(req->object);
+ wake_up_all(&cache->daemon_pollwq);
out:
complete(&req->done);
@@ -222,7 +219,6 @@ static int cachefiles_ondemand_get_fd(struct cachefiles_req *req)
load = (void *)req->msg.data;
load->fd = fd;
- req->msg.object_id = object_id;
object->private->ondemand_id = object_id;
cachefiles_get_unbind_pincount(cache);
@@ -238,6 +234,43 @@ static int cachefiles_ondemand_get_fd(struct cachefiles_req *req)
return ret;
}
+static void ondemand_object_worker(struct work_struct *work)
+{
+ struct cachefiles_object *object =
+ ((struct cachefiles_ondemand_info *)work)->object;
+
+ cachefiles_ondemand_init_object(object);
+}
+
+/*
+ * If there are any inflight or subsequent READ requests on the
+ * closed object, reopen it.
+ * Skip read requests whose related object is reopening.
+ */
+static struct cachefiles_req *cachefiles_ondemand_select_req(struct xa_state *xas,
+ unsigned long xa_max)
+{
+ struct cachefiles_req *req;
+ struct cachefiles_object *object;
+ struct cachefiles_ondemand_info *info;
+
+ xas_for_each_marked(xas, req, xa_max, CACHEFILES_REQ_NEW) {
+ if (req->msg.opcode != CACHEFILES_OP_READ)
+ return req;
+ object = req->object;
+ info = object->private;
+ if (cachefiles_ondemand_object_is_close(object)) {
+ cachefiles_ondemand_set_object_reopening(object);
+ queue_work(fscache_wq, &info->work);
+ continue;
+ } else if (cachefiles_ondemand_object_is_reopening(object)) {
+ continue;
+ }
+ return req;
+ }
+ return NULL;
+}
+
ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
char __user *_buffer, size_t buflen)
{
@@ -248,16 +281,16 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
int ret = 0;
XA_STATE(xas, &cache->reqs, cache->req_id_next);
+ xa_lock(&cache->reqs);
/*
* Cyclically search for a request that has not ever been processed,
* to prevent requests from being processed repeatedly, and make
* request distribution fair.
*/
- xa_lock(&cache->reqs);
- req = xas_find_marked(&xas, UINT_MAX, CACHEFILES_REQ_NEW);
+ req = cachefiles_ondemand_select_req(&xas, ULONG_MAX);
if (!req && cache->req_id_next > 0) {
xas_set(&xas, 0);
- req = xas_find_marked(&xas, cache->req_id_next - 1, CACHEFILES_REQ_NEW);
+ req = cachefiles_ondemand_select_req(&xas, cache->req_id_next - 1);
}
if (!req) {
xa_unlock(&cache->reqs);
@@ -277,14 +310,18 @@ ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
xa_unlock(&cache->reqs);
id = xas.xa_index;
- msg->msg_id = id;
if (msg->opcode == CACHEFILES_OP_OPEN) {
ret = cachefiles_ondemand_get_fd(req);
- if (ret)
+ if (ret) {
+ cachefiles_ondemand_set_object_close(req->object);
goto error;
+ }
}
+ msg->msg_id = id;
+ msg->object_id = req->object->private->ondemand_id;
+
if (copy_to_user(_buffer, msg, n) != 0) {
ret = -EFAULT;
goto err_put_fd;
@@ -317,19 +354,23 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
void *private)
{
struct cachefiles_cache *cache = object->volume->cache;
- struct cachefiles_req *req;
+ struct cachefiles_req *req = NULL;
XA_STATE(xas, &cache->reqs, 0);
int ret;
if (!test_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags))
return 0;
- if (test_bit(CACHEFILES_DEAD, &cache->flags))
- return -EIO;
+ if (test_bit(CACHEFILES_DEAD, &cache->flags)) {
+ ret = -EIO;
+ goto out;
+ }
req = kzalloc(sizeof(*req) + data_len, GFP_KERNEL);
- if (!req)
- return -ENOMEM;
+ if (!req) {
+ ret = -ENOMEM;
+ goto out;
+ }
req->object = object;
init_completion(&req->done);
@@ -367,7 +408,7 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
/* coupled with the barrier in cachefiles_flush_reqs() */
smp_mb();
- if (opcode != CACHEFILES_OP_OPEN &&
+ if (opcode == CACHEFILES_OP_CLOSE &&
!cachefiles_ondemand_object_is_open(object)) {
WARN_ON_ONCE(object->private->ondemand_id == 0);
xas_unlock(&xas);
@@ -392,7 +433,15 @@ static int cachefiles_ondemand_send_req(struct cachefiles_object *object,
wake_up_all(&cache->daemon_pollwq);
wait_for_completion(&req->done);
ret = req->error;
+ kfree(req);
+ return ret;
out:
+ /* Reset the object to close state in error handling path.
+ * If error occurs after creating the anonymous fd,
+ * cachefiles_ondemand_fd_release() will set object to close.
+ */
+ if (opcode == CACHEFILES_OP_OPEN)
+ cachefiles_ondemand_set_object_close(object);
kfree(req);
return ret;
}
@@ -439,7 +488,6 @@ static int cachefiles_ondemand_init_close_req(struct cachefiles_req *req,
if (!cachefiles_ondemand_object_is_open(object))
return -ENOENT;
- req->msg.object_id = object->private->ondemand_id;
trace_cachefiles_ondemand_close(object, &req->msg);
return 0;
}
@@ -455,16 +503,7 @@ static int cachefiles_ondemand_init_read_req(struct cachefiles_req *req,
struct cachefiles_object *object = req->object;
struct cachefiles_read *load = (void *)req->msg.data;
struct cachefiles_read_ctx *read_ctx = private;
- int object_id = object->private->ondemand_id;
-
- /* Stop enqueuing requests when daemon has closed anon_fd. */
- if (!cachefiles_ondemand_object_is_open(object)) {
- WARN_ON_ONCE(object_id == 0);
- pr_info_once("READ: anonymous fd closed prematurely.\n");
- return -EIO;
- }
- req->msg.object_id = object_id;
load->off = read_ctx->off;
load->len = read_ctx->len;
trace_cachefiles_ondemand_read(object, &req->msg, load);
@@ -513,6 +552,7 @@ int cachefiles_ondemand_init_obj_info(struct cachefiles_object *object,
return -ENOMEM;
object->private->object = object;
+ INIT_WORK(&object->private->work, ondemand_object_worker);
return 0;
}
--
2.20.1
Jia Zhu <[email protected]> wrote:
> + struct cachefiles_object *object =
> + ((struct cachefiles_ondemand_info *)work)->object;
container_of().
> + continue;
> + } else if (cachefiles_ondemand_object_is_reopening(object)) {
The "else" is unnecessary.
> +static void ondemand_object_worker(struct work_struct *work)
> +{
> + struct cachefiles_object *object =
> + ((struct cachefiles_ondemand_info *)work)->object;
> +
> + cachefiles_ondemand_init_object(object);
> +}
I can't help but feel there's some missing exclusion/locking. This feels like
it really ought to be driven from the fscache object state machine.
在 2023/3/28 22:12, David Howells 写道:
> Jia Zhu <[email protected]> wrote:
>
>> + struct cachefiles_object *object =
>> + ((struct cachefiles_ondemand_info *)work)->object;
>
> container_of().
Thanks, will revise it.
>
>> + continue;
>> + } else if (cachefiles_ondemand_object_is_reopening(object)) {
>
> The "else" is unnecessary.
Will remove it.
>
>> +static void ondemand_object_worker(struct work_struct *work)
>> +{
>> + struct cachefiles_object *object =
>> + ((struct cachefiles_ondemand_info *)work)->object;
>> +
>> + cachefiles_ondemand_init_object(object);
>> +}
>
> I can't help but feel there's some missing exclusion/locking.
It's indeed kind of complicated here since the async operation.
Thus we paid much attention to catching the race scenarios during coding
and reviewing.
Here are several corner case have been considered:
1. Don't repeatedly push the @work of same object into workqueue:
Use <reopening> state to represent this object. Once the object is
set to <reopening> atomicly, which means the work has been pushed to
workqueue. And other concurrent threads will not pick the <reopening>
object to workqueue.
2. Don't repeatedly set <reopening> state for the same object:
Hold the xa_lock during searching reqs and setting it to <reopening>.
Once object is set to <reopening>, the same object will be skipped.
3. etc.
Would you mind providing more hints for this issue?
> This feels like
> it really ought to be driven from the fscache object state machine.
It's a great idea. But the problem is if we add a new state to indicate
this reopening status and use fscache state machine to drive the cookie
to do reopen(), thus reopen() (in fscache module) ought to invoke
cachefiles_ondemand_init_object() (in cachefile module) to require user
daemon to open the backend file.
But it seems that fscache module should not depend on cachefiles module.
>