Locking issues w/ functionfs gadget and aio?

John Stultz
2015-06-09T01:15:02Z

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