Hi,
On 2023-12-03 at 06:07:43 +0800, Steven Rostedt wrote:
> On Sat, 2 Dec 2023 17:19:25 +0800
> Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> > Hi,
> >
> > 在 2023/12/02 17:01, Edward Adam Davis 写道:
> > > The reproducer involves running test programs on multiple processors separately,
> > > in order to enter blkdev_ioctl() and ultimately reach blk_trace_ioctl() through
> > > two different paths, triggering an AA deadlock.
> > >
> > > CPU0 CPU1
> > > --- ---
> > > mutex_lock(&q->debugfs_mutex) mutex_lock(&q->debugfs_mutex)
> > > mutex_lock(&q->debugfs_mutex) mutex_lock(&q->debugfs_mutex)
> > >
> > >
> > > The first path:
> > > blkdev_ioctl()->
> > > blk_trace_ioctl()->
> > > mutex_lock(&q->debugfs_mutex)
> > >
> > > The second path:
> > > blkdev_ioctl()->
> > > blkdev_common_ioctl()->
> > > blk_trace_ioctl()->
> > > mutex_lock(&q->debugfs_mutex)
> > I still don't understand how this AA deadlock is triggered, does the
> > 'debugfs_mutex' already held before calling blk_trace_ioctl()?
>
> Right, I don't see where the mutex is taken twice. You don't need two
> paths for an AA lock, you only need one.
>
> >
> > >
> > > The solution I have proposed is to exit blk_trace_ioctl() to avoid AA locks if
> > > a task has already obtained debugfs_mutex.
> > >
> > > Fixes: 0d345996e4cb ("x86/kernel: increase kcov coverage under arch/x86/kernel folder")
>
> How does it fix the above? I don't see how the above is even related to this.
I bisected this issue and the following fix information is more accurate:
"
Fixes: f2c2e717642c ("usb: gadget: add raw-gadget interface")
"
All the bisected info is in link: https://github.com/xupengfe/syzkaller_logs/tree/main/231203_140738_blk_trace_ioctl
Acked-by: Pengfei Xu <pengfei.xu@xxxxxxxxx>
Thanks!
>
> -- Steve
>
> > > Reported-and-tested-by: syzbot+ed812ed461471ab17a0c@xxxxxxxxxxxxxxxxxxxxxxxxx
> > > Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
> > > ---
> > > kernel/trace/blktrace.c | 3 ++-
> > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
