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Benjamin Poirier
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net/mlx5: Fix a lockdep warning as part of the write combining test
JIRA: https://issues.redhat.com/browse/RHEL-72226 JIRA: https://issues.redhat.com/browse/RHEL-73517 Upstream-status: v6.13 commit 1b10a51 Author: Yishai Hadas <yishaih@nvidia.com> Date: Wed Jan 15 13:39:05 2025 +0200 net/mlx5: Fix a lockdep warning as part of the write combining test 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: d98995b ("net/mlx5: Reimplement write combining test") Signed-off-by: Yishai Hadas <yishaih@nvidia.com> Reviewed-by: Michael Guralnik <michaelgur@nvidia.com> Reviewed-by: Larysa Zaremba <larysa.zaremba@intel.com> Signed-off-by: Tariq Toukan <tariqt@nvidia.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Benjamin Poirier <bpoirier@redhat.com>
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  • drivers/net/ethernet/mellanox/mlx5/core

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lines changed

‎drivers/net/ethernet/mellanox/mlx5/core/wc.c‎

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -382,6 +382,7 @@ static void mlx5_core_test_wc(struct mlx5_core_dev *mdev)
382382

383383
bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
384384
{
385+
struct mutex *wc_state_lock = &mdev->wc_state_lock;
385386
struct mlx5_core_dev *parent = NULL;
386387

387388
if (!MLX5_CAP_GEN(mdev, bf)) {
@@ -400,32 +401,31 @@ bool mlx5_wc_support_get(struct mlx5_core_dev *mdev)
400401
*/
401402
goto out;
402403

403-
mutex_lock(&mdev->wc_state_lock);
404-
405-
if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
406-
goto unlock;
407-
408404
#ifdef CONFIG_MLX5_SF
409-
if (mlx5_core_is_sf(mdev))
405+
if (mlx5_core_is_sf(mdev)) {
410406
parent = mdev->priv.parent_mdev;
407+
wc_state_lock = &parent->wc_state_lock;
408+
}
411409
#endif
412410

413-
if (parent) {
414-
mutex_lock(&parent->wc_state_lock);
411+
mutex_lock(wc_state_lock);
415412

413+
if (mdev->wc_state != MLX5_WC_STATE_UNINITIALIZED)
414+
goto unlock;
415+
416+
if (parent) {
416417
mlx5_core_test_wc(parent);
417418

418419
mlx5_core_dbg(mdev, "parent set wc_state=%d\n",
419420
parent->wc_state);
420421
mdev->wc_state = parent->wc_state;
421422

422-
mutex_unlock(&parent->wc_state_lock);
423+
} else {
424+
mlx5_core_test_wc(mdev);
423425
}
424426

425-
mlx5_core_test_wc(mdev);
426-
427427
unlock:
428-
mutex_unlock(&mdev->wc_state_lock);
428+
mutex_unlock(wc_state_lock);
429429
out:
430430
mlx5_core_dbg(mdev, "wc_state=%d\n", mdev->wc_state);
431431

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