[RFC PATCH 0/3] tee: optee: Allow to freeze when tee-supplicant is frozen

[Christoph Gellner]

When the system is going to hibernate or suspend it might happen
that the tee-supplicant task is frozen first.
In this case a running OP-TEE task might get stuck in the loop using
wait_for_completion_interruptible to wait for response of tee-supplicant.
    
As a consequence other OP-TEE tasks waiting for the above or a
succeeding stuck OP-TEE task might get stuck as well
- waiting for call queue entry to be completed
- waiting for OPTEE_RPC_WAIT_QUEUE_WAKEUP

This will result in the tasks "refusing to freeze" and
the hibernate or suspend will fail.

OP-TEE issue: https://github.com/OP-TEE/optee_os/issues/4581


- Read back the object
PM: suspend entry (s2idle)
Filesystems sync: 0.000 seconds
Freezing user space processes ...
Freezing of tasks failed after 20.008 seconds (3 tasks refusing to freeze, wq_busy=0):
task:optee_example_s state:R  running task     stack:    0 pid:  124 ppid:     1 flags:0x00000001
[<807d3e24>] (__schedule) from [<841c4000>] (0x841c4000)
task:optee_example_s state:D stack:    0 pid:  126 ppid:     1 flags:0x00000001
[<807d3e24>] (__schedule) from [<807d41d0>] (schedule+0x60/0x120)
[<807d41d0>] (schedule) from [<807d7ffc>] (schedule_timeout+0x1f4/0x340)
[<807d7ffc>] (schedule_timeout) from [<807d56a0>] (wait_for_completion+0x94/0xfc)
[<807d56a0>] (wait_for_completion) from [<80692134>] (optee_cq_wait_for_completion+0x14/0x60)
[<80692134>] (optee_cq_wait_for_completion) from [<806924dc>] (optee_do_call_with_arg+0x14c/0x154)
[<806924dc>] (optee_do_call_with_arg) from [<80692edc>] (optee_shm_unregister+0x78/0xcc)
[<80692edc>] (optee_shm_unregister) from [<80690a9c>] (tee_shm_release+0x88/0x174)
[<80690a9c>] (tee_shm_release) from [<8057f89c>] (dma_buf_release+0x44/0xb0)
[<8057f89c>] (dma_buf_release) from [<8028e4e8>] (__dentry_kill+0x110/0x17c)
[<8028e4e8>] (__dentry_kill) from [<80276cfc>] (__fput+0xc0/0x234)
[<80276cfc>] (__fput) from [<80140b1c>] (task_work_run+0x90/0xbc)
[<80140b1c>] (task_work_run) from [<8010b1c8>] (do_work_pending+0x4a0/0x5a0)
[<8010b1c8>] (do_work_pending) from [<801000cc>] (slow_work_pending+0xc/0x20)
Exception stack(0x843f5fb0 to 0x843f5ff8)
5fa0:                                     00000000 7ef63448 fffffffe 00000000
5fc0: 7ef63448 76f163b0 7ef63448 00000006 7ef63448 7ef634e0 7ef63438 00000000
5fe0: 00000006 7ef63400 76e74833 76dff856 800e0130 00000004
task:optee_example_s state:D stack:    0 pid:  128 ppid:     1 flags:0x00000001
[<807d3e24>] (__schedule) from [<807d41d0>] (schedule+0x60/0x120)
[<807d41d0>] (schedule) from [<807d7ffc>] (schedule_timeout+0x1f4/0x340)
[<807d7ffc>] (schedule_timeout) from [<807d56a0>] (wait_for_completion+0x94/0xfc)
[<807d56a0>] (wait_for_completion) from [<8069359c>] (optee_handle_rpc+0x554/0x710)
[<8069359c>] (optee_handle_rpc) from [<806924cc>] (optee_do_call_with_arg+0x13c/0x154)
[<806924cc>] (optee_do_call_with_arg) from [<80692910>] (optee_invoke_func+0x110/0x190)
[<80692910>] (optee_invoke_func) from [<8068fe3c>] (tee_ioctl+0x113c/0x1244)
[<8068fe3c>] (tee_ioctl) from [<802892ec>] (sys_ioctl+0xe0/0xa24)
[<802892ec>] (sys_ioctl) from [<80100060>] (ret_fast_syscall+0x0/0x54)
Exception stack(0x8424ffa8 to 0x8424fff0)
ffa0:                   00000000 7eb67584 00000003 8010a403 7eb67438 7eb675fc
ffc0: 00000000 7eb67584 7eb67604 00000036 7eb67448 7eb674e0 7eb67438 00000000
ffe0: 76ef7030 7eb6742c 76ee6469 76e83178
OOM killer enabled.
Restarting tasks ... done.
PM: suspend exit
sh: write error: Device or resource busy


The patch set will switch to interruptible waits and add try_to_freeze to allow the waiting
OP-TEE tasks to be frozen as well.

---

In my humble understanding without these patches OP-TEE tasks have only been frozen in user-space.
With these patches it is possible that OP-TEE tasks are frozen although the OP-TEE command
invocation didn't complete.
I'm unable to judge if there are any OP-TEE implementations relying on the fact that suspend won't
happen while the OP-TEE command invocation didn't complete.

The theoretical alternative would be to prevent that tee-supplicant is frozen first.


I was able to reproduce the issue in OP-TEE QEMU v7 using a modified version of
optee_example_secure_storage (loop around REE FS read, support multi-session).
See https://github.com/OP-TEE/optee_os/issues/4581 for details.

After applying these patches (minor adjustments of the includes) I was no longer able to
reproduce the issues.
In my tests OP-TEE QEMU v7 did suspend and resume without troubles.

I'm not able to test on other devices supporting OP-TEE.


I decided to handle each of the locations the OP-TEE task could get stuck as a separate commit.
The downside is that the above call stack doesn't really fit to any of the commits.

Christoph Gellner (3):
  tee: optee: Allow to freeze the task waiting for tee-supplicant
  tee: optee: Allow to freeze while waiting for call_queue
  tee: optee: Allow to freeze while waiting in
    OPTEE_RPC_WAIT_QUEUE_SLEEP

 drivers/tee/optee/call.c | 8 +++++++-
 drivers/tee/optee/rpc.c  | 9 ++++++++-
 drivers/tee/optee/supp.c | 3 +++
 3 files changed, 18 insertions(+), 2 deletions(-)


base-commit: c4681547bcce777daf576925a966ffa824edd09d
-- 
2.32.0.rc0