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>

diff --git a/fs/splice.c b/fs/splice.c
index eefd96b..c5e3c79 100644 (file)
--- 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);