rust: devres: fix race condition due to nesting

Commit f5d3ef25d238 ("rust: devres: get rid of Devres' inner Arc") did
attempt to optimize away the internal reference count of Devres.

However, without an internal reference count, we can't support cases
where Devres is indirectly nested, resulting into a deadlock.

Such indirect nesting easily happens in the following way:

A registration object (which is guarded by devres) hold a reference
count of an object that holds a device resource guarded by devres
itself.

For instance a drm::Registration holds a reference of a drm::Device. The
drm::Device itself holds a device resource in its private data.

When the drm::Registration is dropped by devres, and it happens that it
did hold the last reference count of the drm::Device, it also drops the
device resource, which is guarded by devres itself.

Thus, resulting into a deadlock in the Devres destructor of the device
resource, as in the following backtrace.

	sysrq: Show Blocked State
	task:rmmod           state:D stack:0     pid:1331  tgid:1331  ppid:1330   task_flags:0x400100 flags:0x00000010
	Call trace:
	 __switch_to+0x190/0x294 (T)
	 __schedule+0x878/0xf10
	 schedule+0x4c/0xcc
	 schedule_timeout+0x44/0x118
	 wait_for_common+0xc0/0x18c
	 wait_for_completion+0x18/0x24
	 _RINvNtCs4gKlGRWyJ5S_4core3ptr13drop_in_placeINtNtNtCsgzhNYVB7wSz_6kernel4sync3arc3ArcINtNtBN_6devres6DevresmEEECsRdyc7Hyps3_15rust_driver_pci+0x68/0xe8 [rust_driver_pci]
	 _RINvNvNtCsgzhNYVB7wSz_6kernel6devres16register_foreign8callbackINtNtCs4gKlGRWyJ5S_4core3pin3PinINtNtNtB6_5alloc4kbox3BoxINtNtNtB6_4sync3arc3ArcINtB4_6DevresmEENtNtB1A_9allocator7KmallocEEECsRdyc7Hyps3_15rust_driver_pci+0x34/0xc8 [rust_driver_pci]
	 devm_action_release+0x14/0x20
	 devres_release_all+0xb8/0x118
	 device_release_driver_internal+0x1c4/0x28c
	 driver_detach+0x94/0xd4
	 bus_remove_driver+0xdc/0x11c
	 driver_unregister+0x34/0x58
	 pci_unregister_driver+0x20/0x80
	 __arm64_sys_delete_module+0x1d8/0x254
	 invoke_syscall+0x40/0xcc
	 el0_svc_common+0x8c/0xd8
	 do_el0_svc+0x1c/0x28
	 el0_svc+0x54/0x1d4
	 el0t_64_sync_handler+0x84/0x12c
	 el0t_64_sync+0x198/0x19c

In order to fix this, re-introduce the internal reference count.

Reported-by: Boris Brezillon <boris.brezillon@collabora.com>
Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/.E2.9C.94.20Deadlock.20caused.20by.20nested.20Devres/with/571242651
Reported-by: Markus Probst <markus.probst@posteo.de>
Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/.E2.9C.94.20Devres.20inside.20Devres.20stuck.20on.20cleanup/with/571239721
Reported-by: Alice Ryhl <aliceryhl@google.com>
Closes: https://gitlab.freedesktop.org/panfrost/linux/-/merge_requests/56#note_3282757
Fixes: f5d3ef25d238 ("rust: devres: get rid of Devres' inner Arc")
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Tested-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patch.msgid.link/20260205222529.91465-1-dakr@kernel.org
[ Call clone() prior to devm_add_action(). - Danilo ]
Signed-off-by: Danilo Krummrich <dakr@kernel.org>

0 files changed, 0 insertions, 0 deletions