From: Dan Carpenter <dan.carpenter@linaro.org>
To: Jeff Layton <jlayton@kernel.org>
Cc: ceph-devel@vger.kernel.org, dhowells@redhat.com,
linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [bug report] libceph: add new iov_iter-based ceph_msg_data_type and ceph_osd_data_type
Date: Wed, 11 Oct 2023 16:27:03 +0300 [thread overview]
Message-ID: <b261fcc8-681d-414c-a881-453635c8bd90@kadam.mountain> (raw)
In-Reply-To: <87c8dc9d4734e6e2a0250531bc08140880b4523d.camel@kernel.org>
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
prev parent reply other threads:[~2023-10-11 13:27 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-11 9:50 [bug report] libceph: add new iov_iter-based ceph_msg_data_type and ceph_osd_data_type Dan Carpenter
2023-10-11 12:06 ` Jeff Layton
2023-10-11 13:27 ` Dan Carpenter [this message]
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