Locking issues w/ functionfs gadget and aio?

[John Stultz]

After setting up functionfs for adb w/ 4.1-rc7, I noticed some flakey behavior.
I enabled some lock debugging and got the following:

[   91.648093] read strings
[   91.650264] g_ffs gadget: g_ffs ready
[   91.652551] ci_hdrc ci_hdrc.0: CI_HDRC_CONTROLLER_RESET_EVENT received
[   96.068693] BUG: spinlock lockup suspected on CPU#0, adbd/2791
[   96.068751]  lock: 0xe7764880, .magic: e7764880, .owner: <none>/-1,
.owner_cpu: -407539900
[   96.073448] CPU: 0 PID: 2791 Comm: adbd Not tainted
4.1.0-rc1-00032-g359b12f #147
[   96.081688] Hardware name: Qualcomm (Flattened Device Tree)
[   96.089266] [<c0216ac8>] (unwind_backtrace) from [<c02136a8>]
(show_stack+0x10/0x14)
[   96.094635] [<c02136a8>] (show_stack) from [<c075d9fc>]
(dump_stack+0x70/0xbc)
[   96.102627] [<c075d9fc>] (dump_stack) from [<c026ef90>]
(do_raw_spin_lock+0x114/0x1a0)
[   96.109661] [<c026ef90>] (do_raw_spin_lock) from [<c0764cb8>]
(_raw_spin_lock_irqsave+0x50/0x5c)
[   96.117560] [<c0764cb8>] (_raw_spin_lock_irqsave) from [<c037c1a0>]
(kiocb_set_cancel_fn+0x1c/0x60)
[   96.126519] [<c037c1a0>] (kiocb_set_cancel_fn) from [<c05ae568>]
(ffs_epfile_read_iter+0x8c/0x140)
[   96.135289] [<c05ae568>] (ffs_epfile_read_iter) from [<c0332018>]
(__vfs_read+0xb0/0xd4)
[   96.144290] [<c0332018>] (__vfs_read) from [<c0332ef8>] (vfs_read+0x7c/0x100)
[   96.152535] [<c0332ef8>] (vfs_read) from [<c0332fbc>] (SyS_read+0x40/0x8c)
[   96.159571] [<c0332fbc>] (SyS_read) from [<c020ff20>]
(ret_fast_syscall+0x0/0x4c)
[  117.678633] INFO: rcu_preempt detected stalls on CPUs/tasks:
[  117.683069]  0: (1 GPs behind) idle=805/140000000000000/0
softirq=7187/7189 fqs=2601
[  117.683316]  (detected by 3, t=2603 jiffies, g=3028, c=3027, q=474)
[  117.692345] Task dump for CPU 0:
[  117.697202] adbd            R running      0  2791      1 0x00000002
[  117.704296] [<c075f234>] (__schedule) from [<ffffffff>] (0xffffffff)


It seems we're stuck on the kioctx.ctx_lock, and reviewing that lock
usage I don't see any problems in fs/aio.c right off.

So I'm guessing the f_fs.c code is somehow not initializing the lock
structure, or maybe calling kiocb_set_cancel_fn() from the wrong
context?

Anyway, I was curious if anyone else has seen similar issues or had
suggestions for further debugging.  I've seen this issue as well with
4.1-rc1.

thanks
-john
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