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iov_iter: saner helper for page array allocation 

All call sites of get_pages_array() are essenitally identical now.
Replace with common helper...

Returns number of slots available in resulting array or 0 on OOM;
it's up to the caller to make sure it doesn't ask to zero-entry
array (i.e. neither maxpages nor size are allowed to be zero).

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2022-06-17 14:45:41 -04:00
parent 8520008417
commit 3cf42da327
1 changed files with 32 additions and 45 deletions
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77
lib/iov_iter.c
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@ -1284,9 +1284,20 @@ unsigned long iov_iter_gap_alignment(const struct iov_iter *i)
}
EXPORT_SYMBOL(iov_iter_gap_alignment);
static struct page **get_pages_array(size_t n)
static int want_pages_array(struct page ***res, size_t size,
size_t start, unsigned int maxpages)
{
return kvmalloc_array(n, sizeof(struct page *), GFP_KERNEL);
unsigned int count = DIV_ROUND_UP(size + start, PAGE_SIZE);
if (count > maxpages)
count = maxpages;
WARN_ON(!count); // caller should've prevented that
if (!*res) {
*res = kvmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
if (!*res)
return 0;
}
return count;
}
static ssize_t pipe_get_pages(struct iov_iter *i,
@ -1294,27 +1305,20 @@ static ssize_t pipe_get_pages(struct iov_iter *i,
size_t *start)
{
struct pipe_inode_info *pipe = i->pipe;
unsigned int npages, off;
unsigned int npages, off, count;
struct page **p;
ssize_t left;
int count;
if (!sanity(i))
return -EFAULT;
*start = off = pipe_npages(i, &npages);
count = DIV_ROUND_UP(maxsize + off, PAGE_SIZE);
if (count > npages)
count = npages;
if (count > maxpages)
count = maxpages;
if (!npages)
return -EFAULT;
count = want_pages_array(pages, maxsize, off, min(npages, maxpages));
if (!count)
return -ENOMEM;
p = *pages;
if (!p) {
*pages = p = get_pages_array(count);
if (!p)
return -ENOMEM;
}
left = maxsize;
npages = 0;
if (off) {
@ -1377,9 +1381,8 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
struct page ***pages, size_t maxsize,
unsigned maxpages, size_t *_start_offset)
{
unsigned nr, offset;
pgoff_t index, count;
size_t size = maxsize;
unsigned nr, offset, count;
pgoff_t index;
loff_t pos;
pos = i->xarray_start + i->iov_offset;
@ -1387,16 +1390,9 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i,
offset = pos & ~PAGE_MASK;
*_start_offset = offset;
count = DIV_ROUND_UP(size + offset, PAGE_SIZE);
if (count > maxpages)
count = maxpages;
if (!*pages) {
*pages = get_pages_array(count);
if (!*pages)
return -ENOMEM;
}
count = want_pages_array(pages, maxsize, offset, maxpages);
if (!count)
return -ENOMEM;
nr = iter_xarray_populate_pages(*pages, i->xarray, index, count);
if (nr == 0)
return 0;
@ -1445,7 +1441,7 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
struct page ***pages, size_t maxsize,
unsigned int maxpages, size_t *start)
{
int n, res;
unsigned int n;
if (maxsize > i->count)
maxsize = i->count;
@ -1457,6 +1453,7 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
if (likely(user_backed_iter(i))) {
unsigned int gup_flags = 0;
unsigned long addr;
int res;
if (iov_iter_rw(i) != WRITE)
gup_flags |= FOLL_WRITE;
@ -1466,14 +1463,9 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
addr = first_iovec_segment(i, &maxsize);
*start = addr % PAGE_SIZE;
addr &= PAGE_MASK;
n = DIV_ROUND_UP(maxsize + *start, PAGE_SIZE);
if (n > maxpages)
n = maxpages;
if (!*pages) {
*pages = get_pages_array(n);
if (!*pages)
return -ENOMEM;
}
n = want_pages_array(pages, maxsize, *start, maxpages);
if (!n)
return -ENOMEM;
res = get_user_pages_fast(addr, n, gup_flags, *pages);
if (unlikely(res <= 0))
return res;
@ -1484,15 +1476,10 @@ static ssize_t __iov_iter_get_pages_alloc(struct iov_iter *i,
struct page *page;
page = first_bvec_segment(i, &maxsize, start);
n = DIV_ROUND_UP(maxsize + *start, PAGE_SIZE);
if (n > maxpages)
n = maxpages;
n = want_pages_array(pages, maxsize, *start, maxpages);
if (!n)
return -ENOMEM;
p = *pages;
if (!p) {
*pages = p = get_pages_array(n);
if (!p)
return -ENOMEM;
}
for (int k = 0; k < n; k++)
get_page(*p++ = page++);
return min_t(size_t, maxsize, n * PAGE_SIZE - *start);