Re: Free after use in fw_pm_notify()->kill_requests_without_uevent() due pending_fw_head

[Sodagudi Prasad]

On 2017-01-03 07:19, Greg KH wrote:
> On Tue, Jan 03, 2017 at 06:44:03AM -0800, Sodagudi Prasad wrote:
> > Hi All,
> >
> > Device has crashed due to memory access after free while 
> > pending_fw_head
> > list accessed. Kernel 4.4 stable version is used to reproduce this use 
> > after
> > free.
> > ------------------------------------------------------------------------------------------
> > [ 9031.178428] Unable to handle kernel paging request at virtual 
> > address
> > 6b6b6b6b6b6b6b6b
> > [ 9031.178508] pgd = ffffffc0de9d2000
> > [ 9031.185888] [6b6b6b6b6b6b6b6b] *pgd=0000000000000000,
> > *pud=0000000000000000
> > [ 9031.253045] ------------[ cut here ]------------
> > [ 9031.253100] Kernel BUG at ffffff800864c0a0 [verbose debug info
> > unavailable]
> > [ 9031.256860] Internal error: Oops - BUG: 96000004 [#1] PREEMPT SMP
> > [ 9031.263539] Modules linked in:
> > [ 9031.272708] CPU: 6 PID: 1373 Comm: system_server Tainted: G        
> > W    L
> > 4.4.16+ #1
> > [ 9031.280648] task: ffffffc0d1a1d700 ti: ffffffc0d1a2c000 task.ti:
> > ffffffc0d1a2c000
> > [ 9031.287776] PC is at fw_pm_notify+0x84/0x19c
> > [ 9031.295215] LR is at fw_pm_notify+0x60/0x19c
> > [ 9031.511559] [] fw_pm_notify+0x84/0x19c
> > [ 9031.519355] [] notifier_call_chain+0x58/0x8c
> > [ 9031.524739] [] __blocking_notifier_call_chain+0x54/0x70
> > [ 9031.530387] [] blocking_notifier_call_chain+0x38/0x44
> > [ 9031.537243] [] pm_notifier_call_chain+0x28/0x48
> > [ 9031.543662] [] pm_suspend+0x278/0x674
> > [ 9031.549906] [] state_store+0x58/0x90
> > [ 9031.554942] [] kobj_attr_store+0x18/0x28
> > [ 9031.560154] [] sysfs_kf_write+0x5c/0x68
> > [ 9031.565620] [] kernfs_fop_write+0x114/0x16c
> > [ 9031.571092] [] __vfs_write+0x48/0xf0
> > [ 9031.576816] [] vfs_write+0xb8/0x150
> > [ 9031.581848] [] SyS_write+0x58/0x94
> > [ 9031.586973] [] el0_svc_naked+0x24/0x28
> > -----------------------------------------------------------------------------------------------
> >
> > Kernel panic is observed during device suspend/resume path in the
> > kill_requests_without_uevent() called from fw_pm_notify().
> > when pending_list of a firmware_buf is accessed 0x6b(free pattern) 
> > pattern
> > observed. Based on this firmware_buf is freed even if firmware_buf is 
> > part
> > of
> > pending_fw_head list.
>
> What are you doing in userspace to trigger this problem?  What kernel
> driver is this happening with?
Device continuous suspend and resume is happening here. I think, echo 
mem > /sys/power/state issued here.
It is not clear what driver involved here, because after firmware_buf is 
freed all memory gets filled with 0x6b pattern.

> And 4.4.16 is pretty old, can you try 4.9?
We don't have system which runs on new kernels. Looking for possible 
reasons/path, how firmware_buf can get freed when that in 
pending_fw_head list.

> thanks,
>
> greg k-h

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