On Thu, Mar 06 2025, Bernd Schubert wrote:
> On 3/6/25 12:12, Luis Henriques wrote:
>> When mounting a user-space filesystem using io_uring, the initialization
>> of the rings is done separately in the server side. If for some reason
>> (e.g. a server bug) this step is not performed it will be impossible to
>> unmount the filesystem if there are already requests waiting.
>>
>> This issue is easily reproduced with the libfuse passthrough_ll example,
>> if the queue depth is set to '0' and a request is queued before trying to
>> unmount the filesystem. When trying to force the unmount, fuse_abort_conn()
>> will try to wake up all tasks waiting in fc->blocked_waitq, but because the
>> rings were never initialized, fuse_uring_ready() will never return 'true'.
>>
>> Fixes: 3393ff964e0f ("fuse: block request allocation until io-uring init is complete")
>> Signed-off-by: Luis Henriques <luis@xxxxxxxxxx>
>> ---
>> fs/fuse/dev.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
>> index 7edceecedfa5..2fe565e9b403 100644
>> --- a/fs/fuse/dev.c
>> +++ b/fs/fuse/dev.c
>> @@ -77,7 +77,7 @@ void fuse_set_initialized(struct fuse_conn *fc)
>> static bool fuse_block_alloc(struct fuse_conn *fc, bool for_background)
>> {
>> return !fc->initialized || (for_background && fc->blocked) ||
>> - (fc->io_uring && !fuse_uring_ready(fc));
>> + (fc->io_uring && fc->connected && !fuse_uring_ready(fc));
>> }
>>
>> static void fuse_drop_waiting(struct fuse_conn *fc)
>>
>
> Oh yes, I had missed that.
>
> Reviewed-by: Bernd Schubert <bschubert@xxxxxxx>
Thanks! And... by the way, Bernd:
I know io_uring support in libfuse isn't ready yet, but I think there's
some error handling missing in your uring branch. In particular, the
return of fuse_uring_start() is never checked, and thus if the rings
initialization fails, the server will not get any error.
I found that out because I blindly tried the patch below, and I was
surprised that the server was started just fine.
Cheers,
--
Luís
diff --git a/lib/fuse_uring.c b/lib/fuse_uring.c
index 312aa5dbc735..2258cf0d4259 100644
--- a/lib/fuse_uring.c
+++ b/lib/fuse_uring.c
@@ -498,6 +498,11 @@ static struct fuse_ring_pool *fuse_create_ring(struct fuse_session *se)
fuse_log(FUSE_LOG_DEBUG, "starting io-uring q-depth=%d\n",
se->uring.q_depth);
+ if (!se->uring.q_depth) {
+ fuse_log(FUSE_LOG_ERR, "Invalid ring queue depth value\n");
+ goto err;
+ }
+
fuse_ring = calloc(1, sizeof(*fuse_ring));
if (fuse_ring == NULL) {
fuse_log(FUSE_LOG_ERR, "Allocating the ring failed\n");
