splice: fix repeated kmap()'s in default_file_splice_read()

We cannot reliably map more than one page at the time, or we risk
deadlocking. Just allocate the pages from low mem instead.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 4 insertions, 6 deletions

diff --git a/fs/splice.c b/fs/splice.c
index eefd96b1d7fb..c5e3c79b95a8 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -580,13 +580,13 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
         for (i = 0; i < nr_pages && i < PIPE_BUFFERS && len; i++) {
                 struct page *page;
 
-                page = alloc_page(GFP_HIGHUSER);
+                page = alloc_page(GFP_USER);
                 error = -ENOMEM;
                 if (!page)
                         goto err;
 
                 this_len = min_t(size_t, len, PAGE_CACHE_SIZE - offset);
-                vec[i].iov_base = (void __user *) kmap(page);
+                vec[i].iov_base = (void __user *) page_address(page);
                 vec[i].iov_len = this_len;
                 pages[i] = page;
                 spd.nr_pages++;
@@ -604,7 +604,6 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
 
         nr_freed = 0;
         for (i = 0; i < spd.nr_pages; i++) {
-                kunmap(pages[i]);
                 this_len = min_t(size_t, vec[i].iov_len, res);
                 partial[i].offset = 0;
                 partial[i].len = this_len;
@@ -624,10 +623,9 @@ ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
         return res;
 
 err:
-        for (i = 0; i < spd.nr_pages; i++) {
-                kunmap(pages[i]);
+        for (i = 0; i < spd.nr_pages; i++)
                 __free_page(pages[i]);
-        }
+
         return error;
 }
 EXPORT_SYMBOL(default_file_splice_read);