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Message-ID: <20250113154055.1927008-3-tariqt@nvidia.com>
Date: Mon, 13 Jan 2025 17:40:48 +0200
From: Tariq Toukan <tariqt@...dia.com>
To: "David S. Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, "Andrew
Lunn" <andrew+netdev@...n.ch>
CC: <netdev@...r.kernel.org>, Saeed Mahameed <saeedm@...dia.com>, Gal Pressman
<gal@...dia.com>, Leon Romanovsky <leonro@...dia.com>, Mark Bloch
<mbloch@...dia.com>, Moshe Shemesh <moshe@...dia.com>, Yishai Hadas
<yishaih@...dia.com>, Michael Guralnik <michaelgur@...dia.com>, Tariq Toukan
<tariqt@...dia.com>
Subject: [PATCH net 2/8] net/mlx5: Fix a lockdep warning as part of the write combining test
From: Yishai Hadas <yishaih@...dia.com>
Fix a lockdep warning [1] observed during the write combining test.
The warning indicates a potential nested lock scenario that could lead
to a deadlock.
However, this is a false positive alarm because the SF lock and its
parent lock are distinct ones.
The lockdep confusion arises because the locks belong to the same object
class (i.e., struct mlx5_core_dev).
To resolve this, the code has been refactored to avoid taking both
locks. Instead, only the parent lock is acquired.
[1]
raw_ethernet_bw/2118 is trying to acquire lock:
[ 213.619032] ffff88811dd75e08 (&dev->wc_state_lock){+.+.}-{3:3}, at:
mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.620270]
[ 213.620270] but task is already holding lock:
[ 213.620943] ffff88810b585e08 (&dev->wc_state_lock){+.+.}-{3:3}, at:
mlx5_wc_support_get+0x10c/0x210 [mlx5_core]
[ 213.622045]
[ 213.622045] other info that might help us debug this:
[ 213.622778] Possible unsafe locking scenario:
[ 213.622778]
[ 213.623465] CPU0
[ 213.623815] ----
[ 213.624148] lock(&dev->wc_state_lock);
[ 213.624615] lock(&dev->wc_state_lock);
[ 213.625071]
[ 213.625071] *** DEADLOCK ***
[ 213.625071]
[ 213.625805] May be due to missing lock nesting notation
[ 213.625805]
[ 213.626522] 4 locks held by raw_ethernet_bw/2118:
[ 213.627019] #0: ffff88813f80d578 (&uverbs_dev->disassociate_srcu){.+.+}-{0:0},
at: ib_uverbs_ioctl+0xc4/0x170 [ib_uverbs]
[ 213.628088] #1: ffff88810fb23930 (&file->hw_destroy_rwsem){.+.+}-{3:3},
at: ib_init_ucontext+0x2d/0xf0 [ib_uverbs]
[ 213.629094] #2: ffff88810fb23878 (&file->ucontext_lock){+.+.}-{3:3},
at: ib_init_ucontext+0x49/0xf0 [ib_uverbs]
[ 213.630106] #3: ffff88810b585e08 (&dev->wc_state_lock){+.+.}-{3:3},
at: mlx5_wc_support_get+0x10c/0x210 [mlx5_core]
[ 213.631185]
[ 213.631185] stack backtrace:
[ 213.631718] CPU: 1 UID: 0 PID: 2118 Comm: raw_ethernet_bw Not tainted
6.12.0-rc7_internal_net_next_mlx5_89a0ad0 #1
[ 213.632722] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[ 213.633785] Call Trace:
[ 213.634099]
[ 213.634393] dump_stack_lvl+0x7e/0xc0
[ 213.634806] print_deadlock_bug+0x278/0x3c0
[ 213.635265] __lock_acquire+0x15f4/0x2c40
[ 213.635712] lock_acquire+0xcd/0x2d0
[ 213.636120] ? mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.636722] ? mlx5_ib_enable_lb+0x24/0xa0 [mlx5_ib]
[ 213.637277] __mutex_lock+0x81/0xda0
[ 213.637697] ? mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.638305] ? mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.638902] ? rcu_read_lock_sched_held+0x3f/0x70
[ 213.639400] ? mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.640016] mlx5_wc_support_get+0x18c/0x210 [mlx5_core]
[ 213.640615] set_ucontext_resp+0x68/0x2b0 [mlx5_ib]
[ 213.641144] ? debug_mutex_init+0x33/0x40
[ 213.641586] mlx5_ib_alloc_ucontext+0x18e/0x7b0 [mlx5_ib]
[ 213.642145] ib_init_ucontext+0xa0/0xf0 [ib_uverbs]
[ 213.642679] ib_uverbs_handler_UVERBS_METHOD_GET_CONTEXT+0x95/0xc0
[ib_uverbs]
[ 213.643426] ? _copy_from_user+0x46/0x80
[ 213.643878] ib_uverbs_cmd_verbs+0xa6b/0xc80 [ib_uverbs]
[ 213.644426] ? ib_uverbs_handler_UVERBS_METHOD_INVOKE_WRITE+0x130/0x130
[ib_uverbs]
[ 213.645213] ? __lock_acquire+0xa99/0x2c40
[ 213.645675] ? lock_acquire+0xcd/0x2d0
[ 213.646101] ? ib_uverbs_ioctl+0xc4/0x170 [ib_uverbs]
[ 213.646625] ? reacquire_held_locks+0xcf/0x1f0
[ 213.647102] ? do_user_addr_fault+0x45d/0x770
[ 213.647586] ib_uverbs_ioctl+0xe0/0x170 [ib_uverbs]
[ 213.648102] ? ib_uverbs_ioctl+0xc4/0x170 [ib_uverbs]
[ 213.648632] __x64_sys_ioctl+0x4d3/0xaa0
[ 213.649060] ? do_user_addr_fault+0x4a8/0x770
[ 213.649528] do_syscall_64+0x6d/0x140
[ 213.649947] entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 213.650478] RIP: 0033:0x7fa179b0737b
[ 213.650893] Code: ff ff ff 85 c0 79 9b 49 c7 c4 ff ff ff ff 5b 5d 4c
89 e0 41 5c c3 66 0f 1f 84 00 00 00 00 00 f3 0f 1e fa b8
10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d
7d 2a 0f 00 f7 d8 64 89 01 48
[ 213.652619] RSP: 002b:00007ffd2e6d46e8 EFLAGS: 00000246 ORIG_RAX:
0000000000000010
[ 213.653390] RAX: ffffffffffffffda RBX: 00007ffd2e6d47f8 RCX:
00007fa179b0737b
[ 213.654084] RDX: 00007ffd2e6d47e0 RSI: 00000000c0181b01 RDI:
0000000000000003
[ 213.654767] RBP: 00007ffd2e6d47c0 R08: 00007fa1799be010 R09:
0000000000000002
[ 213.655453] R10: 00007ffd2e6d4960 R11: 0000000000000246 R12:
00007ffd2e6d487c
[ 213.656170] R13: 0000000000000027 R14: 0000000000000001 R15:
00007ffd2e6d4f70
Fixes: d98995b4bf98 ("net/mlx5: Reimplement write combining test")
Signed-off-by: Yishai Hadas <yishaih@...dia.com>
Reviewed-by: Michael Guralnik <michaelgur@...dia.com>
Signed-off-by: Tariq Toukan <tariqt@...dia.com>
---
drivers/net/ethernet/mellanox/mlx5/core/wc.c | 24 ++++++++++----------
1 file changed, 12 insertions(+), 12 deletions(-)
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/wc.c b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
index 1bed75eca97d..740b719e7072 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/wc.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/wc.c
@@ -382,6 +382,7 @@ static void mlx5_core_test_wc(struct mlx5_core_dev *mdev)
bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
{
+ struct mutex *wc_state_lock = &mdev->wc_state_lock;
struct mlx5_core_dev *parent = NULL;
if (!MLX5_CAP_GEN(mdev, bf)) {
@@ -400,32 +401,31 @@ bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
*/
goto out;
- mutex_lock(&mdev->wc_state_lock);
-
- if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
- goto unlock;
-
#ifdef CONFIG_MLX5_SF
- if (mlx5_core_is_sf(mdev))
+ if (mlx5_core_is_sf(mdev)) {
parent = mdev->priv.parent_mdev;
+ wc_state_lock = &parent->wc_state_lock;
+ }
#endif
- if (parent) {
- mutex_lock(&parent->wc_state_lock);
+ mutex_lock(wc_state_lock);
+ if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
+ goto unlock;
+
+ if (parent) {
mlx5_core_test_wc(parent);
mlx5_core_dbg(mdev, "parent set wc_state=%d\n",
parent->wc_state);
mdev->wc_state = parent->wc_state;
- mutex_unlock(&parent->wc_state_lock);
+ } else {
+ mlx5_core_test_wc(mdev);
}
- mlx5_core_test_wc(mdev);
-
unlock:
- mutex_unlock(&mdev->wc_state_lock);
+ mutex_unlock(wc_state_lock);
out:
mlx5_core_dbg(mdev, "wc_state=%d\n", mdev->wc_state);
--
2.45.0
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