On Wed, Oct 11, 2023 at 08:06:59AM -0400, Jeff Layton wrote:
> On Wed, 2023-10-11 at 12:50 +0300, Dan Carpenter wrote:
> > Hello Jeff Layton,
> >
> > To be honest, I'm not sure why I am only seeing this now. These
> > warnings are hard to analyse because they involve such a long call tree.
> > Anyway, hopefully it's not too complicated for you since you know the
> > code.
> >
> > The patch dee0c5f83460: "libceph: add new iov_iter-based
> > ceph_msg_data_type and ceph_osd_data_type" from Jul 1, 2022
> > (linux-next), leads to the following Smatch static checker warning:
> >
> > lib/iov_iter.c:905 want_pages_array()
> > warn: sleeping in atomic context
> >
> > lib/iov_iter.c
> > 896 static int want_pages_array(struct page ***res, size_t size,
> > 897 size_t start, unsigned int maxpages)
> > 898 {
> > 899 unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE);
> > 900
> > 901 if (count > maxpages)
> > 902 count = maxpages;
> > 903 WARN_ON(!count); // caller should've prevented that
> > 904 if (!*res) {
> > --> 905 *res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
> > 906 if (!*res)
> > 907 return 0;
> > 908 }
> > 909 return count;
> > 910 }
> >
> >
> > prep_next_sparse_read() <- disables preempt
> > -> advance_cursor()
> > -> ceph_msg_data_next()
> > -> ceph_msg_data_iter_next()
> > -> iov_iter_get_pages2()
> > -> __iov_iter_get_pages_alloc()
> > -> want_pages_array()
> >
> > The prep_next_sparse_read() functions hold the spin_lock(&o->o_requests_lock);
> > lock so it can't sleep. But iov_iter_get_pages2() seems like a sleeping
> > operation.
> >
> >
>
> I think this is a false alarm, but I'd appreciate a sanity check:
>
> iov_iter_get_pages2 has this:
>
> BUG_ON(!pages);
>
> ...which should ensure that *res won't be NULL when want_pages_array is
> called. That said, this seems like kind of a fragile thing to rely on.
> Should we do something to make this a bit less subtle?
Nah, forget about it. Let's just leave this conversation up on lore so
if anyone has questions about it they can read this thread. The
BUG_ON(!pages) is really straight forward to understand.
regards,
dan carpenter
