On Sat, 2 Dec 2023 17:19:25 +0800
Yu Kuai <[email protected]> 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.
-- Steve
> > Reported-and-tested-by:
> > [email protected]
> > Signed-off-by: Edward Adam Davis <[email protected]>
> > ---
> > kernel/trace/blktrace.c | 3 ++-
> > 1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
