[PATCH 5.17 0867/1126] nvme-tcp: lockdep: annotate in-kernel sockets

Greg Kroah-Hartman
2022-04-05T08:36:17Z

From: Chris Leech <cleech@redhat.com>

[ Upstream commit 841aee4d75f18fdfb53935080b03de0c65e9b92c ]

Put NVMe/TCP sockets in their own class to avoid some lockdep warnings.
Sockets created by nvme-tcp are not exposed to user-space, and will not
trigger certain code paths that the general socket API exposes.

Lockdep complains about a circular dependency between the socket and
filesystem locks, because setsockopt can trigger a page fault with a
socket lock held, but nvme-tcp sends requests on the socket while file
system locks are held.

======================================================
WARNING: possible circular locking dependency detected
5.15.0-rc3 #1 Not tainted
------------------------------------------------------
fio/1496 is trying to acquire lock:
(sk_lock-AF_INET){+.+.}-{0:0}, at: tcp_sendpage+0x23/0x80

but task is already holding lock:
(&xfs_dir_ilock_class/5){+.+.}-{3:3}, at: xfs_ilock+0xcf/0x290 [xfs]

which lock already depends on the new lock.

other info that might help us debug this:

chain exists of:
sk_lock-AF_INET --> sb_internal --> &xfs_dir_ilock_class/5

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&xfs_dir_ilock_class/5);
lock(sb_internal);
lock(&xfs_dir_ilock_class/5);
lock(sk_lock-AF_INET);

*** DEADLOCK ***

6 locks held by fio/1496:
#0: (sb_writers#13){.+.+}-{0:0}, at: path_openat+0x9fc/0xa20
#1: (&inode->i_sb->s_type->i_mutex_dir_key){++++}-{3:3}, at: path_openat+0x296/0xa20
#2: (sb_internal){.+.+}-{0:0}, at: xfs_trans_alloc_icreate+0x41/0xd0 [xfs]
#3: (&xfs_dir_ilock_class/5){+.+.}-{3:3}, at: xfs_ilock+0xcf/0x290 [xfs]
#4: (hctx->srcu){....}-{0:0}, at: hctx_lock+0x51/0xd0
#5: (&queue->send_mutex){+.+.}-{3:3}, at: nvme_tcp_queue_rq+0x33e/0x380 [nvme_tcp]

This annotation lets lockdep analyze nvme-tcp controlled sockets
independently of what the user-space sockets API does.

Link: https://lore.kernel.org/linux-nvme/CAHj4cs9MDYLJ+q+2_GXUK9HxFizv2pxUryUR0toX974M040z7g@mail.gmail.com/

Signed-off-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/nvme/host/tcp.c | 40 ++++++++++++++++++++++++++++++++++++++++
1 file changed, 40 insertions(+)

diff --git a/drivers/nvme/host/tcp.c b/drivers/nvme/host/tcp.c
index 65e00c64a588..d66e2de044e0 100644
--- a/drivers/nvme/host/tcp.c
+++ b/drivers/nvme/host/tcp.c
@@ -30,6 +30,44 @@ static int so_priority;
module_param(so_priority, int, 0644);
MODULE_PARM_DESC(so_priority, "nvme tcp socket optimize priority");

+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+/* lockdep can detect a circular dependency of the form
+ * sk_lock -> mmap_lock (page fault) -> fs locks -> sk_lock
+ * because dependencies are tracked for both nvme-tcp and user contexts. Using
+ * a separate class prevents lockdep from conflating nvme-tcp socket use with
+ * user-space socket API use.
+ */
+static struct lock_class_key nvme_tcp_sk_key[2];
+static struct lock_class_key nvme_tcp_slock_key[2];
+
+static void nvme_tcp_reclassify_socket(struct socket *sock)
+{
+ struct sock *sk = sock->sk;
+
+ if (WARN_ON_ONCE(!sock_allow_reclassification(sk)))
+ return;
+
+ switch (sk->sk_family) {
+ case AF_INET:
+ sock_lock_init_class_and_name(sk, "slock-AF_INET-NVME",
+ &nvme_tcp_slock_key[0],
+ "sk_lock-AF_INET-NVME",
+ &nvme_tcp_sk_key[0]);
+ break;
+ case AF_INET6:
+ sock_lock_init_class_and_name(sk, "slock-AF_INET6-NVME",
+ &nvme_tcp_slock_key[1],
+ "sk_lock-AF_INET6-NVME",
+ &nvme_tcp_sk_key[1]);
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ }
+}
+#else
+static void nvme_tcp_reclassify_socket(struct socket *sock) { }
+#endif
+
enum nvme_tcp_send_state {
NVME_TCP_SEND_CMD_PDU = 0,
NVME_TCP_SEND_H2C_PDU,
@@ -1469,6 +1507,8 @@ static int nvme_tcp_alloc_queue(struct nvme_ctrl *nctrl,
goto err_destroy_mutex;
}

+ nvme_tcp_reclassify_socket(queue->sock);
+
/* Single syn retry */
tcp_sock_set_syncnt(queue->sock->sk, 1);

--
2.34.1