Re: [PATCH] aio: Wake all waiters when destroying ctx

From: Andrew Morton
Date: Fri Mar 11 2011 - 19:20:38 EST


On Fri, 11 Mar 2011 09:21:46 -0500
Jeff Moyer <jmoyer@xxxxxxxxxx> wrote:

> Roland Dreier <roland@xxxxxxxxxx> writes:
>
> > From: Roland Dreier <roland@xxxxxxxxxxxxxxx>
> >
> > The test program below will hang because io_getevents() uses
> > add_wait_queue_exclusive(), which means the wake_up() in io_destroy()
> > only wakes up one of the threads. Fix this by using wake_up_all() in
> > the aio code paths where we want to make sure no one gets stuck.
>
> [snip]
>
> > Cc: <stable@xxxxxxxxxx>
> > Signed-off-by: Roland Dreier <roland@xxxxxxxxxxxxxxx>
> > ---
> > fs/aio.c | 4 ++--
> > 1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/aio.c b/fs/aio.c
> > index 26869cd..88f0ed5 100644
> > --- a/fs/aio.c
> > +++ b/fs/aio.c
> > @@ -520,7 +520,7 @@ static inline void really_put_req(struct kioctx *ctx, struct kiocb *req)
> > ctx->reqs_active--;
> >
> > if (unlikely(!ctx->reqs_active && ctx->dead))
> > - wake_up(&ctx->wait);
> > + wake_up_all(&ctx->wait);
> > }
> >
> > static void aio_fput_routine(struct work_struct *data)
> > @@ -1229,7 +1229,7 @@ static void io_destroy(struct kioctx *ioctx)
> > * by other CPUs at this point. Right now, we rely on the
> > * locking done by the above calls to ensure this consistency.
> > */
> > - wake_up(&ioctx->wait);
> > + wake_up_all(&ioctx->wait);
> > put_ioctx(ioctx); /* once for the lookup */
> > }
> >
>
> Thanks, Roland, this looks good.
>
> Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>

It's a fairly old bug (yes?) and we're presumably close to 2.6.38. So
I scheduled the fix for 2.6.39 marked for backporting into 2.6.38.x and
earlier.

That may have been a bit over-cautious - feel free to argue ;)
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