On Tuesday 31 July 2012 15:42:51 Alan Stern wrote:
> On Tue, 31 Jul 2012, Oliver Neukum wrote:
>
> > > Another alternative is for the other drivers to delay the reset (by
> > > sleeping in their pre_reset callbacks) until they can handle the reset
> > > safely.
> >
> > No! You must not ever do that!
> >
> > The reset is a part of the error handling path of the block layer. Therefore
> > it must not sleep indefinitely. In particular you must never wait for
> > anything
> > user space does or for any part of the kernel that allocates memory with
> > GFP_KERNEL or GFP_NOFS, and you must allocate memory only with GFP_NOIO.
> > The penalty is deadlock.
>
> True; it's easy to forget that. Although in practice it's not very
> likely to occur. It would require a writable memory-mapped file or
> swap partition on a USB drive and a system running low on available
> memory.
If you refer to allocating memory, yes.
Waiting for user space is worse. Any read access to the storage device
would deadlock.
Regards
Oliver
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