From: Leon Romanovsky <leon@kernel.org>
To: Kamal Heib <kheib@redhat.com>
Cc: linux-rdma@vger.kernel.org,
Potnuri Bharat Teja <bharat@chelsio.com>,
Jason Gunthorpe <jgg@ziepe.ca>
Subject: Re: [PATCH for-next] RDMA/cxgb4: Fix possible circular locking dependency
Date: Sun, 19 Oct 2025 14:26:43 +0300 [thread overview]
Message-ID: <20251019112643.GF6199@unreal> (raw)
In-Reply-To: <20251008192837.481193-1-kheib@redhat.com>
On Wed, Oct 08, 2025 at 03:28:37PM -0400, Kamal Heib wrote:
> Holding dev_mutex across c4iw_remove() during module exit can lead to a
> lockdep warning and potential deadlock. The RDMA core takes global
> locks (e.g. devices_rwsem) inside ib_unregister_device(), which may
> conflict with the locking order used elsewhere in the driver.
>
> ======================================================
> WARNING: possible circular locking dependency detected
> 6.12.0-124.5.1.el10_1.x86_64+debug #1 Not tainted
> ------------------------------------------------------
> rmmod/3524 is trying to acquire lock:
> ffffffffc1c0dd18 (devices_rwsem){++++}-{4:4}, at: disable_device+0xaf/0x240 [ib_core]
>
> but task is already holding lock:
> ffff889104e44708 (&device->unregistration_lock){+.+.}-{4:4}, at: __ib_unregister_device+0x209/0x460 [ib_core]
>
> which lock already depends on the new lock.
>
> the existing dependency chain (in reverse order) is:
>
> -> #6 (&device->unregistration_lock){+.+.}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> __mutex_lock+0x18b/0x12b0
> __ib_unregister_device+0x209/0x460 [ib_core]
> ib_unregister_device+0x25/0x30 [ib_core]
> c4iw_remove+0xce/0xda [iw_cxgb4]
> c4iw_exit_module+0x7d/0xe0 [iw_cxgb4]
> __do_sys_delete_module.isra.0+0x33a/0x540
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #5 (dev_mutex){+.+.}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> __mutex_lock+0x18b/0x12b0
> c4iw_uld_add+0x137/0x500 [iw_cxgb4]
> uld_attach+0x908/0xd80 [cxgb4]
> cxgb4_uld_alloc_resources.part.0+0x364/0x1120 [cxgb4]
> cxgb4_register_uld+0x10c/0x400 [cxgb4]
> c4iw_init_module+0x77/0x80 [iw_cxgb4]
> do_one_initcall+0xa5/0x260
> do_init_module+0x238/0x7c0
> init_module_from_file+0xdf/0x150
> idempotent_init_module+0x230/0x770
> __x64_sys_finit_module+0xbe/0x130
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #4 (uld_mutex){+.+.}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> __mutex_lock+0x18b/0x12b0
> cxgb_up+0x24/0xee0 [cxgb4]
> cxgb_open+0x7e/0x250 [cxgb4]
> __dev_open+0x241/0x420
> __dev_change_flags+0x44c/0x660
> dev_change_flags+0x80/0x160
> do_setlink+0x1acd/0x23e0
> __rtnl_newlink+0xb07/0xe40
> rtnl_newlink+0x62/0x90
> rtnetlink_rcv_msg+0x2f3/0xb20
> netlink_rcv_skb+0x13d/0x3b0
> netlink_unicast+0x42e/0x720
> netlink_sendmsg+0x765/0xc20
> ____sys_sendmsg+0x974/0xc60
> ___sys_sendmsg+0xfd/0x180
> __sys_sendmsg+0xe8/0x190
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #3 (rtnl_mutex){+.+.}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> __mutex_lock+0x18b/0x12b0
> ib_get_eth_speed+0xee/0x9d0 [ib_core]
> ib_query_port+0x140/0x1f0 [ib_core]
> ib_setup_port_attrs+0x1a5/0x4c0 [ib_core]
> add_one_compat_dev+0x4bd/0x7b0 [ib_core]
> rdma_dev_init_net+0x257/0x3e0 [ib_core]
> ops_init+0x109/0x300
> setup_net+0x1c4/0x730
> copy_net_ns+0x23b/0x540
> create_new_namespaces+0x358/0x920
> unshare_nsproxy_namespaces+0x8a/0x1b0
> ksys_unshare+0x2df/0x740
> __x64_sys_unshare+0x31/0x40
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #2 (&device->compat_devs_mutex){+.+.}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> __mutex_lock+0x18b/0x12b0
> add_one_compat_dev+0xe0/0x7b0 [ib_core]
> rdma_dev_init_net+0x257/0x3e0 [ib_core]
> ops_init+0x109/0x300
> setup_net+0x1c4/0x730
> copy_net_ns+0x23b/0x540
> create_new_namespaces+0x358/0x920
> unshare_nsproxy_namespaces+0x8a/0x1b0
> ksys_unshare+0x2df/0x740
> __x64_sys_unshare+0x31/0x40
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #1 (rdma_nets_rwsem){++++}-{4:4}:
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> down_read+0xa3/0x4b0
> enable_device_and_get+0x26b/0x350 [ib_core]
> ib_register_device+0x1c3/0x4f0 [ib_core]
> bnxt_re_ib_init+0x433/0x530 [bnxt_re]
> bnxt_re_add_device+0x60d/0x760 [bnxt_re]
> bnxt_re_probe+0xcf/0x140 [bnxt_re]
> auxiliary_bus_probe+0xa1/0xf0
> really_probe+0x1e0/0x8a0
> __driver_probe_device+0x18c/0x370
> driver_probe_device+0x4a/0x120
> __driver_attach+0x194/0x4a0
> bus_for_each_dev+0x106/0x190
> bus_add_driver+0x2a1/0x4d0
> driver_register+0x1a5/0x360
> __auxiliary_driver_register+0x152/0x240
> c4iw_init_module+0x43/0x80 [iw_cxgb4]
> do_one_initcall+0xa5/0x260
> do_init_module+0x238/0x7c0
> init_module_from_file+0xdf/0x150
> idempotent_init_module+0x230/0x770
> __x64_sys_finit_module+0xbe/0x130
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> -> #0 (devices_rwsem){++++}-{4:4}:
> check_prev_add+0xf1/0xce0
> validate_chain+0x481/0x560
> __lock_acquire+0x559/0xb80
> lock_acquire.part.0+0xbe/0x270
> down_write+0x99/0x220
> disable_device+0xaf/0x240 [ib_core]
> __ib_unregister_device+0x26f/0x460 [ib_core]
> ib_unregister_device+0x25/0x30 [ib_core]
> c4iw_remove+0xce/0xda [iw_cxgb4]
> c4iw_exit_module+0x7d/0xe0 [iw_cxgb4]
> __do_sys_delete_module.isra.0+0x33a/0x540
> do_syscall_64+0x92/0x180
> entry_SYSCALL_64_after_hwframe+0x76/0x7e
>
> other info that might help us debug this:
>
> Chain exists of:
> devices_rwsem --> dev_mutex --> &device->unregistration_lock
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock(&device->unregistration_lock);
> lock(dev_mutex);
> lock(&device->unregistration_lock);
> lock(devices_rwsem);
>
> *** DEADLOCK ***
>
> This patch fixes the issue by moving all uld_ctx entries from the global
> uld_ctx_list to a temporary local list while holding dev_mutex, then
> releasing the mutex before calling c4iw_remove() and freeing the
> contexts. This prevents any lock inversion while safely avoiding races
> on the shared list.
>
> Signed-off-by: Kamal Heib <kheib@redhat.com>
> ---
> drivers/infiniband/hw/cxgb4/device.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/hw/cxgb4/device.c b/drivers/infiniband/hw/cxgb4/device.c
> index d892f55febe2..fe902e2f3b0d 100644
> --- a/drivers/infiniband/hw/cxgb4/device.c
> +++ b/drivers/infiniband/hw/cxgb4/device.c
> @@ -1554,14 +1554,18 @@ static int __init c4iw_init_module(void)
> static void __exit c4iw_exit_module(void)
> {
> struct uld_ctx *ctx, *tmp;
> + LIST_HEAD(local_list);
>
> mutex_lock(&dev_mutex);
> - list_for_each_entry_safe(ctx, tmp, &uld_ctx_list, entry) {
> + list_splice_init(&uld_ctx_list, &local_list);
> + mutex_unlock(&dev_mutex);
It doesn't make any sense to hold this mutex. You are calling to remove
cxgb4 module and worry about running probe at the same time. It
shouldn't happen. This lock can be removed.
Thanks
> +
> + list_for_each_entry_safe(ctx, tmp, &local_list, entry) {
> + list_del(&ctx->entry);
> if (ctx->dev)
> c4iw_remove(ctx);
> kfree(ctx);
> }
> - mutex_unlock(&dev_mutex);
> destroy_workqueue(reg_workq);
> cxgb4_unregister_uld(CXGB4_ULD_RDMA);
> c4iw_cm_term();
> --
> 2.51.0
>
prev parent reply other threads:[~2025-10-19 11:26 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-08 19:28 [PATCH for-next] RDMA/cxgb4: Fix possible circular locking dependency Kamal Heib
2025-10-19 11:26 ` Leon Romanovsky [this message]
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