Re: [Bug report] Memory leak in scmi_device_create

[Cristian Marussi <cristian.marussi@arm.com>]

On Thu, Mar 06, 2025 at 11:09:33AM +0000, Alice Ryhl wrote:
> On Wed, Mar 05, 2025 at 05:10:16PM +0000, Cristian Marussi wrote:
> > On Wed, Mar 05, 2025 at 11:59:58AM +0000, Alice Ryhl wrote:
> > > Dear SYSTEM CONTROL & POWER/MANAGEMENT INTERFACE (SCPI/SCMI) Message
> > > Protocol drivers maintainers,
> > > 
> > > I flashed a v6.13-rc3 kernel onto a Rock5B board and noticed the
> > > following output in my terminal:
> > > 
> > > [  687.694465] kmemleak: 4 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> > > 
> > > It seems that there is a memory leak for devices created with
> > > scmi_device_create.
> > > 
> > `
> > Hi Alice,
> > 
> > thanks for this report.
> > 
> > > This was with a kernel running v6.13-rc3, but as far as I can tell, no
> > > relevant changes have landed since v6.13-rc3. My tree *does* include
> > > commit 295416091e44 ("firmware: arm_scmi: Fix slab-use-after-free in
> > > scmi_bus_notifier()"). I've only seen this kmemleak report once, so it's
> > > not happening consistently.
> > > 
> > > See below for the full kmemleak report.
> > > 
> > > Alice
> > > 
> > > $ sudo cat /sys/kernel/debug/kmemleak
> > > unreferenced object 0xffffff8106c86000 (size 2048):
> > >   comm "swapper/0", pid 1, jiffies 4294893094
> > >   hex dump (first 32 bytes):
> > >     02 00 00 00 10 00 00 00 c0 01 bc 03 81 ff ff ff  ................
> > >     60 67 ba 03 81 ff ff ff 18 60 c8 06 81 ff ff ff  `g.......`......
> > >   backtrace (crc feae9680):
> > >     [<00000000197aa008>] kmemleak_alloc+0x34/0xa0
> > >     [<0000000056fe02c9>] __kmalloc_cache_noprof+0x1e0/0x450
> > >     [<00000000a8b3dfe1>] __scmi_device_create+0xb4/0x2b4
> > >     [<000000008714917b>] scmi_device_create+0x40/0x194
> > >     [<000000001818f3cf>] scmi_chan_setup+0x144/0x3b8
> > >     [<00000000970bad38>] scmi_probe+0x584/0xa78
> > >     [<000000002600d2fd>] platform_probe+0xbc/0xf0
> > >     [<00000000f6f556b4>] really_probe+0x1b8/0x520
> > >     [<00000000eed93d59>] __driver_probe_device+0xe0/0x1d8
> > >     [<00000000d613b754>] driver_probe_device+0x6c/0x208
> > >     [<00000000187a9170>] __driver_attach+0x168/0x328
> > >     [<00000000e3ff1834>] bus_for_each_dev+0x14c/0x178
> > >     [<00000000984a3176>] driver_attach+0x34/0x44
> > >     [<00000000fc35bf2a>] bus_add_driver+0x1bc/0x358
> > >     [<00000000747fce19>] driver_register+0xc0/0x1a0
> > >     [<0000000081cb8754>] __platform_driver_register+0x40/0x50
> > > unreferenced object 0xffffff8103bc01c0 (size 32):
> > 
> > I could not reproduce on my setup, even though I run a system with
> > all the existent SCMI protocols (and related drivers) enabled (and
> > so a lot of device creations) and a downstream test driver that causes
> > even more SCMI devices to be created/destroyed at load/unload.
> > 
> > Coming down the path from scmi_chan_setup(), it seems something around
> > transport devices creation, but it is not obvious to me where the leak
> > could hide....
> > 
> > ...any particular setup on your side ? ...using LKMs, loading/unloading,
> > any usage pattern that could help me reproduce ?
> 
> I looked into this a bit more, and actually it does happen consistently.
> It's just that kmemleak doesn't report it until 10 minutes after
> booting, so I did not notice it.
> 
> As for my setup, well, I boot the kernel over pxe and the rootfs is
> mounted over NFSv4. The memory leak happens even if I don't do anything
> at all - I just boot and wait. The device is a Radxa Rock5B.
> 
> Not sure what other information there is to give.
> 

My question as stated above was mainly to understand if the SCMI stack
was built-in or compiled as loadable modules (lsmod|grep -i scmi)...
...I am just to try to pin down a possible 'more-vulnerable' configuration..
..I could not see any report even triggering a kmemleak scan on v6.14-rc5
BUT I only tested with a fully built-in SCMI stack indeed as of now...so
the question.

> I tried again with v6.14-rc5, and I still got the leak:

Ok...thanks I will investigate with different configs.

Thanks,
Cristian