[PATCH v10 16/17] fuse: block request allocation until io-uring init is complete

Bernd Schubert
2025-01-20T01:29:26Z

From: Bernd Schubert <bernd@bsbernd.com>

Avoid races and block request allocation until io-uring
queues are ready.

This is a especially important for background requests,
as bg request completion might cause lock order inversion
of the typical queue->lock and then fc->bg_lock

fuse_request_end
spin_lock(&fc->bg_lock);
flush_bg_queue
fuse_send_one
fuse_uring_queue_fuse_req
spin_lock(&queue->lock);

Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
---
fs/fuse/dev.c | 3 ++-
fs/fuse/dev_uring.c | 3 +++
fs/fuse/fuse_i.h | 3 +++
fs/fuse/inode.c | 2 ++
4 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 1b593b23f7b8c319ec38c7e726dabf516965500e..f002e8a096f97ba8b6e039309292942995c901c5 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -76,7 +76,8 @@ 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);
+ return !fc->initialized || (for_background && fc->blocked) ||
+ (fc->io_uring && !fuse_uring_ready(fc));
}

static void fuse_drop_waiting(struct fuse_conn *fc)
diff --git a/fs/fuse/dev_uring.c b/fs/fuse/dev_uring.c
index fcce03174ee18153d597e9cd1a2659b1c237e3eb..1249c7fd4d63692413d103e72eaa5e502188d3bc 100644
--- a/fs/fuse/dev_uring.c
+++ b/fs/fuse/dev_uring.c
@@ -957,6 +957,7 @@ static void fuse_uring_do_register(struct fuse_ring_ent *ent,
if (ready) {
WRITE_ONCE(fiq->ops, &fuse_io_uring_ops);
WRITE_ONCE(ring->ready, true);
+ wake_up_all(&fc->blocked_waitq);
}
}
}
@@ -1130,6 +1131,8 @@ int __maybe_unused fuse_uring_cmd(struct io_uring_cmd *cmd,
if (err) {
pr_info_once("FUSE_IO_URING_CMD_REGISTER failed err=%d\n",
err);
+ fc->io_uring = 0;
+ wake_up_all(&fc->blocked_waitq);
return err;
}
break;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index e71556894bc25808581424ec7bdd4afeebc81f15..886c3af2195892cb2ca0a171cd7b930b6e92484c 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -867,6 +867,9 @@ struct fuse_conn {
/* Use pages instead of pointer for kernel I/O */
unsigned int use_pages_for_kvec_io:1;

+ /* Use io_uring for communication */
+ unsigned int io_uring;
+
/** Maximum stack depth for passthrough backing files */
int max_stack_depth;

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 328797b9aac9a816a4ad2c69b6880dc6ef6222b0..e9db2cb8c150878634728685af0fa15e7ade628f 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -1390,6 +1390,8 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
else
ok = false;
}
+ if (flags & FUSE_OVER_IO_URING && fuse_uring_enabled())
+ fc->io_uring = 1;
} else {
ra_pages = fc->max_read / PAGE_SIZE;
fc->no_lock = 1;

--
2.43.0