Re: [BUG] ALSA: seq: a possible sleep-in-atomic-context bug in snd_virmidi_dev_receive_event()

[Jia-Ju Bai]

On 2019/12/17 21:37, Takashi Iwai wrote:
> On Tue, 17 Dec 2019 14:24:21 +0100,
> Jia-Ju Bai wrote:
> > The driver may sleep while holding a read lock.
> > The function call path (from bottom to top) in Linux 4.19 is:
> >
> > sound/core/seq/seq_memory.c, 96:
> >  ÂÂÂ copy_from_user in snd_seq_dump_var_event
> > sound/core/seq/seq_virmidi.c, 97:
> >  ÂÂÂ snd_seq_dump_var_event in snd_virmidi_dev_receive_event
> > sound/core/seq/seq_virmidi.c, 88:
> >  ÂÂÂ _raw_read_lock in snd_virmidi_dev_receive_event
> This can't happen.  snd_virmidi_dev_receive_event() takes
> conditionally either read_lock or rw_sem depending on the atomic
> argument.  And the data including user-space pointer is handled always
> with atomic=1, hence down_read() is used instead of read_lock() here.

Okay, thanks for the explanation.


Best wishes,
Jia-Ju Bai