Re: Deadlock in 2.2 sock_alloc_send_skb?

[Andrea Arcangeli]

On Thu, May 10, 2001 at 07:30:47PM +0200, Andi Kleen wrote:
> On Thu, May 10, 2001 at 01:57:49PM +0100, Alan Cox wrote:
> > > If that happens, and the socket uses GFP_ATOMIC allocation, the while (1)
> > > loop in sock_alloc_send_skb() will endlessly spin, without ever calling
> > > schedule(), and all the time holding the kernel lock ...
> > 
> > If the socket is using GFP_ATOMIC allocation it should never loop. That is
> > -not-allowed-. 
> 
> It is just not clear why any socket should use GFP_ATOMIC. I can understand
> it using GFP_BUFFER e.g. for nbd, but GFP_ATOMIC seems to be rather radical
> and fragile.

side note, the only legal use of GFP_ATOMIC in sock_alloc_send_skb is
with noblock set and fallback zero, remeber GFP_BUFFER will sleep, it
may not sleep in vanilla 2.2.19 but the necessary lowlatency hooks in
the memory balancing that for example I have on my 2.2 tree will make it
to sleep.

The patch self contained looks perfect (I didn't checked that the
callers are happy with a -ENOMEM errorcode though), if alloc_skb()
failed that's a plain -ENOMEM. The caller must _not_ try again, they
must take a recovery fail path instead.

Andrea