!! This is an RFC patch - hence sign-off absence !!
This bug happens only when the UDC needs to sleep during usb_ep_dequeue,
as is the case for (at least) dwc3.
RFC:
- I do not understand what eps_lock is supposed to protect in original
ffs_aio_cancel implementation, especially once one considers
usb_ep_dequeue should be allowed to sleep: no non-intricated locking
scheme would allow this. I removed this lock, I may be doing something
wrong.
- Because the 3 other locks also disable interrupts, I believe the only
valid fix is to move usb_ep_dequeue to another call stack.
Not being sure I could safely reuse ffs_io_data.work (completion
function will be called during usb_ep_dequeue call, so during
ffs_aio_cancel_worker call), I added a new work_struct.
I believe it is safe to deffer cancellation from io_data point of view,
as ffs owns its buffer, and from aio point of view as regular io_cancel
return -EINPROGRESS when kiocb_cancel succeeds, implying kiocb_cancel
is not required to be fully effective synchronously.
Sadly, kiocb_set_cancel_fn is only used in ffs and its legacy
counterpart, so I have very little precedents to look at.
read_buffer gets freed in ffs_func_eps_disable, but it does not matter
for AIO, only synchronous reads use it.
Are there more checks needed ?
- This change should have no effect on existing cancel/complete race
condition, which I expect is already handled in AIO. If not, then it's
yet another ffs_aio_cancel bug, and this commit will get larger...
- Should anything be done with the return value of usb_ep_dequeue in
ffs_aio_cancel_worker ? Failures to cancel because transfer is already
completed or not known should be harmless, but could there be more
serious issues lurking ?
[ 382.200896] BUG: scheduling while atomic: screen/1808/0x00000100
[ 382.207124] 4 locks held by screen/1808:
[ 382.211266] #0: (rcu_callback){....}, at: [<c10b4ff0>] rcu_process_callbacks+0x260/0x440
[ 382.219949] #1: (rcu_read_lock_sched){....}, at: [<c1358ba0>] percpu_ref_switch_to_atomic_rcu+0xb0/0x130
[ 382.230034] #2: (&(&ctx->ctx_lock)->rlock){....}, at: [<c11f0c73>] free_ioctx_users+0x23/0xd0
[ 382.230096] #3: (&(&ffs->eps_lock)->rlock){....}, at: [<f81e7710>] ffs_aio_cancel+0x20/0x60 [usb_f_fs]
[ 382.230160] Modules linked in: usb_f_fs libcomposite configfs bnep btsdio bluetooth ecdh_generic brcmfmac brcmutil intel_powerclamp coretemp dwc3 kvm_intel ulpi udc_core kvm irqbypass crc32_pclmul crc32c_intel pcbc dwc3_pci aesni_intel aes_i586 crypto_simd cryptd ehci_pci ehci_hcd gpio_keys usbcore basincove_gpadc industrialio usb_common
[ 382.230407] CPU: 1 PID: 1808 Comm: screen Not tainted 4.14.0-edison+ #117
[ 382.230416] Hardware name: Intel Corporation Merrifield/BODEGA BAY, BIOS 542 2015.01.21:18.19.48
[ 382.230425] Call Trace:
[ 382.230438] <SOFTIRQ>
[ 382.230466] dump_stack+0x47/0x62
[ 382.230498] __schedule_bug+0x61/0x80
[ 382.230522] __schedule+0x43/0x7a0
[ 382.230587] schedule+0x5f/0x70
[ 382.230625] dwc3_gadget_ep_dequeue+0x14c/0x270 [dwc3]
[ 382.230669] ? do_wait_intr_irq+0x70/0x70
[ 382.230724] usb_ep_dequeue+0x19/0x90 [udc_core]
[ 382.230770] ffs_aio_cancel+0x37/0x60 [usb_f_fs]
[ 382.230798] kiocb_cancel+0x31/0x40
[ 382.230822] free_ioctx_users+0x4d/0xd0
[ 382.230858] percpu_ref_switch_to_atomic_rcu+0x10a/0x130
[ 382.230881] ? percpu_ref_exit+0x40/0x40
[ 382.230904] rcu_process_callbacks+0x2b3/0x440
[ 382.230965] __do_softirq+0xf8/0x26b
[ 382.231011] ? __softirqentry_text_start+0x8/0x8
[ 382.231033] do_softirq_own_stack+0x22/0x30
[ 382.231042] </SOFTIRQ>
[ 382.231071] irq_exit+0x45/0xc0
[ 382.231089] smp_apic_timer_interrupt+0x13c/0x150
[ 382.231118] apic_timer_interrupt+0x35/0x3c
[ 382.231132] EIP: __copy_user_ll+0xe2/0xf0
[ 382.231142] EFLAGS: 00210293 CPU: 1
[ 382.231154] EAX: bfd4508c EBX: 00000004 ECX: 00000003 EDX: f3d8fe50
[ 382.231165] ESI: f3d8fe51 EDI: bfd4508d EBP: f3d8fe14 ESP: f3d8fe08
[ 382.231176] DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
[ 382.231265] core_sys_select+0x25f/0x320
[ 382.231346] ? __wake_up_common_lock+0x62/0x80
[ 382.231399] ? tty_ldisc_deref+0x13/0x20
[ 382.231438] ? ldsem_up_read+0x1b/0x40
[ 382.231459] ? tty_ldisc_deref+0x13/0x20
[ 382.231479] ? tty_write+0x29f/0x2e0
[ 382.231514] ? n_tty_ioctl+0xe0/0xe0
[ 382.231541] ? tty_write_unlock+0x30/0x30
[ 382.231566] ? __vfs_write+0x22/0x110
[ 382.231604] ? security_file_permission+0x2f/0xd0
[ 382.231635] ? rw_verify_area+0xac/0x120
[ 382.231677] ? vfs_write+0x103/0x180
[ 382.231711] SyS_select+0x87/0xc0
[ 382.231739] ? SyS_write+0x42/0x90
[ 382.231781] do_fast_syscall_32+0xd6/0x1a0
[ 382.231836] entry_SYSENTER_32+0x47/0x71
[ 382.231848] EIP: 0xb7f75b05
[ 382.231857] EFLAGS: 00000246 CPU: 1
[ 382.231868] EAX: ffffffda EBX: 00000400 ECX: bfd4508c EDX: bfd4510c
[ 382.231878] ESI: 00000000 EDI: 00000000 EBP: 00000000 ESP: bfd45020
[ 382.231889] DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 007b
[ 382.232281] softirq: huh, entered softirq 9 RCU c10b4d90 with preempt_count 00000100, exited with 00000000?
---
drivers/usb/gadget/function/f_fs.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index c56f7afb841a..3f80b2208bca 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -219,6 +219,7 @@ struct ffs_io_data {
struct mm_struct *mm;
struct work_struct work;
+ struct work_struct cancellation_work;
struct usb_ep *ep;
struct usb_request *req;
@@ -1072,23 +1073,30 @@ ffs_epfile_open(struct inode *inode, struct file *file)
return 0;
}
+static void ffs_aio_cancel_worker(struct work_struct *work)
+{
+ struct ffs_io_data *io_data = container_of(work, struct ffs_io_data,
+ cancellation_work);
+ ENTER();
+
+ usb_ep_dequeue(io_data->ep, io_data->req);
+}
+
static int ffs_aio_cancel(struct kiocb *kiocb)
{
struct ffs_io_data *io_data = kiocb->private;
- struct ffs_epfile *epfile = kiocb->ki_filp->private_data;
+ struct ffs_data *ffs = io_data->ffs;
int value;
ENTER();
- spin_lock_irq(&epfile->ffs->eps_lock);
-
- if (likely(io_data && io_data->ep && io_data->req))
- value = usb_ep_dequeue(io_data->ep, io_data->req);
- else
+ if (likely(io_data && io_data->ep && io_data->req)) {
+ INIT_WORK(&io_data->cancellation_work, ffs_aio_cancel_worker);
+ queue_work(ffs->io_completion_wq, &io_data->cancellation_work);
+ value = -EINPROGRESS;
+ } else
value = -EINVAL;
- spin_unlock_irq(&epfile->ffs->eps_lock);
-
return value;
}
--
2.15.0
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