This issue was found when adbd trying to open functionfs with AIO mode.
Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable
adbd with AIO mode on Android.
When adbd is opening functionfs, it will try to read 24 bytes at the
fisrt read I/O control. If this reading has been failed, adbd will
try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO
mode, functionfs will be acted with asyncronized I/O path. After the
successful read transfer has been completed by gadget hardware, the
following series of functions will be called.
ffs_epfile_async_io_complete() -> ffs_user_copy_worker() ->
copy_to_iter() -> _copy_to_iter() -> copyout() ->
iterate_and_advance() -> iterate_iovec()
Adding debug trace to these functions, it has been found that in
iterate_iovec(), the calculation result of n will be turned into zero.
n = wanted - n; /* 0 == n = 24 - 24; */
Which causes copyout() won't copy data to userspace since the length
to be copied "v.iov_len" will be zero, which isn't correct. This also
leads ffs_copy_to_iter() always return -EFAULT. Finally adbd cannot
open functionfs and send FUNCTIONFS_CLEAR_HALT.
Signed-off-by: Macpaul Lin <[email protected]>
---
lib/iov_iter.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index fb29c02c6a3c..f9334144e259 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -36,7 +36,8 @@
skip = __v.iov_len; \
n -= __v.iov_len; \
} \
- n = wanted - n; \
+ if (n != wanted) \
+ n = wanted - n; \
}
#define iterate_kvec(i, n, __v, __p, skip, STEP) { \
--
2.18.0
On Tue, Feb 18, 2020 at 03:41:12PM +0800, Macpaul Lin wrote:
> This issue was found when adbd trying to open functionfs with AIO mode.
> Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable
> adbd with AIO mode on Android.
>
> When adbd is opening functionfs, it will try to read 24 bytes at the
> fisrt read I/O control. If this reading has been failed, adbd will
> try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO
> mode, functionfs will be acted with asyncronized I/O path. After the
> successful read transfer has been completed by gadget hardware, the
> following series of functions will be called.
> ffs_epfile_async_io_complete() -> ffs_user_copy_worker() ->
> copy_to_iter() -> _copy_to_iter() -> copyout() ->
> iterate_and_advance() -> iterate_iovec()
>
> Adding debug trace to these functions, it has been found that in
> iterate_iovec(), the calculation result of n will be turned into zero.
> n = wanted - n; /* 0 == n = 24 - 24; */
> Which causes copyout() won't copy data to userspace since the length
> to be copied "v.iov_len" will be zero, which isn't correct. This also
> leads ffs_copy_to_iter() always return -EFAULT. Finally adbd cannot
> open functionfs and send FUNCTIONFS_CLEAR_HALT.
>
> Signed-off-by: Macpaul Lin <[email protected]>
> ---
> lib/iov_iter.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index fb29c02c6a3c..f9334144e259 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -36,7 +36,8 @@
> skip = __v.iov_len; \
> n -= __v.iov_len; \
> } \
> - n = wanted - n; \
> + if (n != wanted) \
> + n = wanted - n; \
> }
First of all, nothing in that line can possibly *cause*
copyout() to do anything - it's after the calls of step. What's
more, this changes behaviour only when wanted would've been equal to
n, doesn't it? Which translates into "no decrements of n have
happened at all", i.e. "nothing has been copied". IOW, it's
a consequence of no copyout, not the cause of such. You can
make copy_to_iter() lie and pretend if has copied everything
when it has copied nothing, but that won't change the underlying
bug.
So I'm afraid your debugging is not finished - you
still need to find out what causes the copyout failures and/or
BS iov_iter padded by caller.
On Tue, 2020-02-18 at 12:41 +0000, Al Viro wrote:
> On Tue, Feb 18, 2020 at 03:41:12PM +0800, Macpaul Lin wrote:
> > This issue was found when adbd trying to open functionfs with AIO mode.
> > Usually, we need to set "setprop sys.usb.ffs.aio_compat 0" to enable
> > adbd with AIO mode on Android.
> >
> > When adbd is opening functionfs, it will try to read 24 bytes at the
> > fisrt read I/O control. If this reading has been failed, adbd will
> > try to send FUNCTIONFS_CLEAR_HALT to functionfs. When adbd is in AIO
> > mode, functionfs will be acted with asyncronized I/O path. After the
> > successful read transfer has been completed by gadget hardware, the
> > following series of functions will be called.
> > ffs_epfile_async_io_complete() -> ffs_user_copy_worker() ->
> > copy_to_iter() -> _copy_to_iter() -> copyout() ->
> > iterate_and_advance() -> iterate_iovec()
> >
> > Adding debug trace to these functions, it has been found that in
> > iterate_iovec(), the calculation result of n will be turned into zero.
> > n = wanted - n; /* 0 == n = 24 - 24; */
> > Which causes copyout() won't copy data to userspace since the length
> > to be copied "v.iov_len" will be zero, which isn't correct. This also
> > leads ffs_copy_to_iter() always return -EFAULT. Finally adbd cannot
> > open functionfs and send FUNCTIONFS_CLEAR_HALT.
> >
> > Signed-off-by: Macpaul Lin <[email protected]>
> > ---
> > lib/iov_iter.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> > index fb29c02c6a3c..f9334144e259 100644
> > --- a/lib/iov_iter.c
> > +++ b/lib/iov_iter.c
> > @@ -36,7 +36,8 @@
> > skip = __v.iov_len; \
> > n -= __v.iov_len; \
> > } \
> > - n = wanted - n; \
> > + if (n != wanted) \
> > + n = wanted - n; \
> > }
>
> First of all, nothing in that line can possibly *cause*
> copyout() to do anything - it's after the calls of step. What's
> more, this changes behaviour only when wanted would've been equal to
> n, doesn't it? Which translates into "no decrements of n have
> happened at all", i.e. "nothing has been copied". IOW, it's
> a consequence of no copyout, not the cause of such. You can
> make copy_to_iter() lie and pretend if has copied everything
> when it has copied nothing, but that won't change the underlying
> bug.
>
> So I'm afraid your debugging is not finished - you
> still need to find out what causes the copyout failures and/or
> BS iov_iter padded by caller.
Thanks for your explanation. After these days, I've found this issue
only happened on arm 64-bit system, while arm 32-bit system works well.
After more debugging, it looks like arm 64 tagged ABI related issue.
I've update a new patch here:
usb: gadget: f_fs: try to fix AIO issue under ARM 64 bit TAGGED mode
https://lkml.org/lkml/2020/2/23/16.
Thanks.
Macpaul Lin.