[PATCH rdma-next] RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency

[Edward Srouji <edwards@nvidia.com>]

From: Or Har-Toov <ohartoov@nvidia.com>

Commit 51976c6cd786 ("RDMA/core: Provide rdma_user_mmap_disassociate()
to disassociate mmap pages") introduced disassociation_lock to protect
new mmap registrations against uverbs_user_mmap_disassociate(), but
created an ABBA deadlock:

  Thread A (mmap / fork):
    mmap_lock -> disassociation_lock

  Thread B (disassociate):
    disassociation_lock -> mmap_lock

Fix by removing disassociation_lock entirely and using the pre-existing
hw_destroy_rwsem instead. hw_destroy_rwsem already provides the same
protection: rdma_umap_open() and ib_uverbs_mmap() both use
down_read_trylock() before registering a new VMA, so holding hw_destroy_rwsem
in uverbs_user_mmap_disassociate() is sufficient to block new registrations.
trylock is used in both mmap paths (not blocking down_read) because
mmap_lock is already held on entry, and uverbs_user_mmap_disassociate()
acquires mmap_lock internally — a blocking read would recreate the same
deadlock.

The only caller that was not taking hw_destroy_rwsem for write was
rdma_user_mmap_disassociate(). Fix it to take the rwsem per-ufile while
iterating under lists_mutex.  This is safe because ib_uverbs_close()
releases hw_destroy_rwsem entirely before acquiring lists_mutex, so the
two locks are never held simultaneously.

lockdep warning:

 [  776.654252] ======================================================
 [  776.655214] WARNING: possible circular locking dependency detected
 [  776.656167] 6.18.0for-upstream_debug_94e244d9ccab #1 Not tainted
 [  776.657114] ------------------------------------------------------
 [  776.658087] devlink/14824 is trying to acquire lock:
 [  776.658879] ffff88811170c800 (&mm->mmap_lock){++++}-{4:4}, at: uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
 [  776.660479]
 [  776.660479] but task is already holding lock:
 [  776.661460] ffff888142d92b08 (&file->disassociation_lock){+.+.}-{4:4}, at: uverbs_user_mmap_disassociate+0x39/0x780 [ib_uverbs]
 [  776.663177]
 [  776.663177] which lock already depends on the new lock.
 [  776.663177]
 [  776.664525]
 [  776.664525] the existing dependency chain (in reverse order) is:
 [  776.665724]
 [  776.665724] -> #2 (&file->disassociation_lock){+.+.}-{4:4}:
 [  776.666887]        __mutex_lock+0x16d/0x2330
 [  776.667633]        rdma_umap_open+0x129/0x280 [ib_uverbs]
 [  776.668489]        dup_mmap+0xa40/0x1790
 [  776.669170]        copy_process+0x5dd2/0x6170
 [  776.669933]        kernel_clone+0xb6/0x610
 [  776.670636]        __do_sys_clone+0xb5/0xf0
 [  776.671354]        do_syscall_64+0x70/0x12e0
 [  776.672083]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
 [  776.672940]
 [  776.672940] -> #1 (&mm->mmap_lock/1){+.+.}-{4:4}:
 [  776.673985]        down_write_nested+0x90/0x1e0
 [  776.674751]        dup_mmap+0x201/0x1790
 [  776.675448]        copy_process+0x5dd2/0x6170
 [  776.676180]        kernel_clone+0xb6/0x610
 [  776.676904]        __do_sys_clone+0xb5/0xf0
 [  776.677615]        do_syscall_64+0x70/0x12e0
 [  776.678351]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
 [  776.679239]
 [  776.679239] -> #0 (&mm->mmap_lock){++++}-{4:4}:
 [  776.680253]        __lock_acquire+0x18c6/0x2ec0
 [  776.681018]        lock_acquire+0x10e/0x2e0
 [  776.681742]        down_read+0x95/0x430
 [  776.682395]        uverbs_user_mmap_disassociate+0x168/0x780 [ib_uverbs]
 [  776.683436]        uverbs_destroy_ufile_hw+0x1ae/0x270 [ib_uverbs]
 [  776.684416]        ib_uverbs_remove_one+0x22b/0x420 [ib_uverbs]
 [  776.685371]        remove_client_context+0xa6/0xf0 [ib_core]
 [  776.686342]        disable_device+0x12b/0x240 [ib_core]
 [  776.687249]        __ib_unregister_device+0x269/0x460 [ib_core]
 [  776.688233]        ib_unregister_device+0x21/0x30 [ib_core]
 [  776.689140]        mlx5r_remove+0xd0/0x170 [mlx5_ib]
 [  776.689999]        device_release_driver_internal+0x3b2/0x560
 [  776.694876]        bus_remove_device+0x1f5/0x3e0
 [  776.695638]        device_del+0x3b9/0x990
 [  776.696329]        mlx5_detach_device+0x17e/0x350 [mlx5_core]
 [  776.697429]        mlx5_unload_one_devl_locked+0x3f/0xb0 [mlx5_core]
 [  776.698578]        mlx5_devlink_reload_down+0x1f9/0x550 [mlx5_core]
 [  776.699712]        devlink_reload+0x13e/0x680
 [  776.700456]        devlink_nl_reload_doit+0xc29/0x1160
 [  776.701293]        genl_family_rcv_msg_doit+0x1c9/0x2a0
 [  776.702135]        genl_rcv_msg+0x3f0/0x6b0
 [  776.702854]        netlink_rcv_skb+0x11d/0x370
 [  776.703605]        genl_rcv+0x24/0x40
 [  776.704236]        netlink_unicast+0x5b4/0x970
 [  776.704984]        netlink_sendmsg+0x730/0xbf0
 [  776.705748]        __sock_sendmsg+0xc5/0x190
 [  776.706461]        __sys_sendto+0x201/0x2f0
 [  776.707188]        __x64_sys_sendto+0xdc/0x1b0
 [  776.707931]        do_syscall_64+0x70/0x12e0
 [  776.708643]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
 [  776.709546]
 [  776.709546] other info that might help us debug this:
 [  776.709546]
 [  776.710910] Chain exists of:
 [  776.710910]   &mm->mmap_lock --> &mm->mmap_lock/1 --> &file->disassociation_lock
 [  776.710910]
 [  776.712805]  Possible unsafe locking scenario:
 [  776.712805]
 [  776.713828]        CPU0                    CPU1
 [  776.714589]        ----                    ----
 [  776.715347]   lock(&file->disassociation_lock);
 [  776.716097]                                lock(&mm->mmap_lock/1);
 [  776.717067]                                lock(&file->disassociation_lock);
 [  776.718199]   rlock(&mm->mmap_lock);
 [  776.718857]
 [  776.718857]  *** DEADLOCK ***

Fixes: 51976c6cd786 ("RDMA/core: Provide rdma_user_mmap_disassociate() to disassociate mmap pages")
Signed-off-by: Or Har-Toov <ohartoov@nvidia.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Edward Srouji <edwards@nvidia.com>
---
 drivers/infiniband/core/rdma_core.c   |  1 -
 drivers/infiniband/core/uverbs_main.c | 25 +++++++++++--------------
 include/rdma/uverbs_types.h           |  2 --
 3 files changed, 11 insertions(+), 17 deletions(-)

diff --git a/drivers/infiniband/core/rdma_core.c b/drivers/infiniband/core/rdma_core.c
index fd5651c003aed3178188b4f89ede86d893676a9a..a7cbe643e33c6e5247a8f4eebc3b8ab1d9a66e4f 100644
--- a/drivers/infiniband/core/rdma_core.c
+++ b/drivers/infiniband/core/rdma_core.c
@@ -69,7 +69,6 @@ void ib_uverbs_release_file(struct kref *ref)
 
 	if (file->disassociate_page)
 		__free_pages(file->disassociate_page, 0);
-	mutex_destroy(&file->disassociation_lock);
 	mutex_destroy(&file->umap_lock);
 	mutex_destroy(&file->ucontext_lock);
 	kfree(file);
diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 3ccf58e96aedebb6f8886ef5b8fad5660475c4c7..5be21fca4948272b9a66e8ee357ca9432556c887 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -643,12 +643,15 @@ static int ib_uverbs_mmap(struct file *filp, struct vm_area_struct *vma)
 		goto out;
 	}
 
-	mutex_lock(&file->disassociation_lock);
+	if (!down_read_trylock(&file->hw_destroy_rwsem)) {
+		ret = -EIO;
+		goto out;
+	}
 
 	vma->vm_ops = &rdma_umap_ops;
 	ret = ucontext->device->ops.mmap(ucontext, vma);
 
-	mutex_unlock(&file->disassociation_lock);
+	up_read(&file->hw_destroy_rwsem);
 out:
 	srcu_read_unlock(&file->device->disassociate_srcu, srcu_key);
 	return ret;
@@ -670,7 +673,6 @@ static void rdma_umap_open(struct vm_area_struct *vma)
 	/* We are racing with disassociation */
 	if (!down_read_trylock(&ufile->hw_destroy_rwsem))
 		goto out_zap;
-	mutex_lock(&ufile->disassociation_lock);
 
 	/*
 	 * Disassociation already completed, the VMA should already be zapped.
@@ -683,12 +685,10 @@ static void rdma_umap_open(struct vm_area_struct *vma)
 		goto out_unlock;
 	rdma_umap_priv_init(priv, vma, opriv->entry);
 
-	mutex_unlock(&ufile->disassociation_lock);
 	up_read(&ufile->hw_destroy_rwsem);
 	return;
 
 out_unlock:
-	mutex_unlock(&ufile->disassociation_lock);
 	up_read(&ufile->hw_destroy_rwsem);
 out_zap:
 	/*
@@ -772,7 +772,7 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
 {
 	struct rdma_umap_priv *priv, *next_priv;
 
-	mutex_lock(&ufile->disassociation_lock);
+	lockdep_assert_held_write(&ufile->hw_destroy_rwsem);
 
 	while (1) {
 		struct mm_struct *mm = NULL;
@@ -798,10 +798,8 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
 			break;
 		}
 		mutex_unlock(&ufile->umap_lock);
-		if (!mm) {
-			mutex_unlock(&ufile->disassociation_lock);
+		if (!mm)
 			return;
-		}
 
 		/*
 		 * The umap_lock is nested under mmap_lock since it used within
@@ -831,8 +829,6 @@ void uverbs_user_mmap_disassociate(struct ib_uverbs_file *ufile)
 		mmap_read_unlock(mm);
 		mmput(mm);
 	}
-
-	mutex_unlock(&ufile->disassociation_lock);
 }
 
 /**
@@ -850,8 +846,11 @@ void rdma_user_mmap_disassociate(struct ib_device *device)
 
 	mutex_lock(&uverbs_dev->lists_mutex);
 	list_for_each_entry(ufile, &uverbs_dev->uverbs_file_list, list) {
-		if (ufile->ucontext)
+		if (ufile->ucontext) {
+			down_write(&ufile->hw_destroy_rwsem);
 			uverbs_user_mmap_disassociate(ufile);
+			up_write(&ufile->hw_destroy_rwsem);
+		}
 	}
 	mutex_unlock(&uverbs_dev->lists_mutex);
 }
@@ -926,8 +925,6 @@ static int ib_uverbs_open(struct inode *inode, struct file *filp)
 	mutex_init(&file->umap_lock);
 	INIT_LIST_HEAD(&file->umaps);
 
-	mutex_init(&file->disassociation_lock);
-
 	filp->private_data = file;
 	list_add_tail(&file->list, &dev->uverbs_file_list);
 	mutex_unlock(&dev->lists_mutex);
diff --git a/include/rdma/uverbs_types.h b/include/rdma/uverbs_types.h
index 5a07f9a6dcd1f6e2faaf2df25d2661d5bf2a170e..6f3622892c0cc6d71890f4ece7bd3a0c59432ee2 100644
--- a/include/rdma/uverbs_types.h
+++ b/include/rdma/uverbs_types.h
@@ -180,8 +180,6 @@ struct ib_uverbs_file {
 	struct page *disassociate_page;
 
 	struct xarray		idr;
-
-	struct mutex disassociation_lock;
 };
 
 extern const struct uverbs_obj_type_class uverbs_idr_class;

---
base-commit: a12d9145145b21c50531afb6e3f711b1f34e1465
change-id: 20260811-fix-mmap-lockdep-91da89a3f37c

Best regards,
-- 
Edward Srouji <edwards@nvidia.com>