[PATCH] iov_iter: Four fixes for ITER_XARRAY

David Howells
2021-04-25T23:15:05Z

Hi Al,

I think this patch should include all the fixes necessary. I could merge
it in, but I think it might be better to tag it on the end as an additional
patch.

David
---
iov_iter: Four fixes for ITER_XARRAY

Fix four things[1] in the patch that adds ITER_XARRAY[2]:

(1) Remove the address_space struct predeclaration. This is a holdover
from when it was ITER_MAPPING.

(2) Fix _copy_mc_to_iter() so that the xarray segment updates count and
iov_offset in the iterator before returning.

(3) Fix iov_iter_alignment() to not loop in the xarray case. Because the
middle pages are all whole pages, only the end pages need be
considered - and this can be reduced to just looking at the start
position in the xarray and the iteration size.

(4) Fix iov_iter_advance() to limit the size of the advance to no more
than the remaining iteration size.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/YIVrJT8GwLI0Wlgx@zeniv-ca.linux.org.uk [1]
Link: https://lore.kernel.org/r/161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk [2]
---
include/linux/uio.h | 1 -
lib/iov_iter.c | 5 +++++
2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 5f5ffc45d4aa..d3ec87706d75 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -10,7 +10,6 @@
#include <uapi/linux/uio.h>

struct page;
-struct address_space;
struct pipe_inode_info;

struct kvec {
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 44fa726a8323..61228a6c69f8 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -791,6 +791,8 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
curr_addr = (unsigned long) from;
bytes = curr_addr - s_addr - rem;
rcu_read_unlock();
+ i->iov_offset += bytes;
+ i->count -= bytes;
return bytes;
}
})
@@ -1147,6 +1149,7 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
return;
}
if (unlikely(iov_iter_is_xarray(i))) {
+ size = min(size, i->count);
i->iov_offset += size;
i->count -= size;
return;
@@ -1346,6 +1349,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
return size | i->iov_offset;
return size;
}
+ if (unlikely(iov_iter_is_xarray(i)))
+ return (i->xarray_start + i->iov_offset) | i->count;
iterate_all_kinds(i, size, v,
(res |= (unsigned long)v.iov_base | v.iov_len, 0),
res |= v.bv_offset | v.bv_len,