[PATCH rdma-next] RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency
From: Edward Srouji
Date: Tue Aug 11 2026 - 13:19:32 EST
From: Or Har-Toov <ohartoov@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leonro@xxxxxxxxxx>
Signed-off-by: Edward Srouji <edwards@xxxxxxxxxx>
---
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@xxxxxxxxxx>