squashfs: don't use intermediate buffer if pages missing

Now that the "page actor" can handle missing pages, we don't have to fall
back to using an intermediate buffer in Squashfs_readpage_block() if all
the pages necessary can't be obtained.

Link: https://lkml.kernel.org/r/20220611032133.5743-3-phillip@squashfs.org.uk
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Xiongwei Song <Xiongwei.Song@windriver.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
index 5af5802..be4b12d 100644 (file)
--- a/fs/squashfs/file_direct.c
+++ b/fs/squashfs/file_direct.c
@@ -18,9 +18,6 @@
 #include "squashfs.h"
 #include "page_actor.h"
 
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-       int pages, struct page **page, int bytes);
-
 /* Read separately compressed datablock directly into page cache */
 int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
        int expected)
@@ -33,7 +30,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
        int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
        int start_index = target_page->index & ~mask;
        int end_index = start_index | mask;
-       int i, n, pages, missing_pages, bytes, res = -ENOMEM;
+       int i, n, pages, bytes, res = -ENOMEM;
        struct page **page;
        struct squashfs_page_actor *actor;
        void *pageaddr;
@@ -48,44 +45,29 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
                return res;
 
        /* Try to grab all the pages covered by the Squashfs block */
-       for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
+       for (i = 0, n = start_index; n <= end_index; n++) {
                page[i] = (n == target_page->index) ? target_page :
                        grab_cache_page_nowait(target_page->mapping, n);
 
-               if (page[i] == NULL) {
-                       missing_pages++;
+               if (page[i] == NULL)
                        continue;
-               }
 
                if (PageUptodate(page[i])) {
                        unlock_page(page[i]);
                        put_page(page[i]);
-                       page[i] = NULL;
-                       missing_pages++;
+                       continue;
                }
-       }
-
-       if (missing_pages) {
-               /*
-                * Couldn't get one or more pages, this page has either
-                * been VM reclaimed, but others are still in the page cache
-                * and uptodate, or we're racing with another thread in
-                * squashfs_readpage also trying to grab them.  Fall back to
-                * using an intermediate buffer.
-                */
-               res = squashfs_read_cache(target_page, block, bsize, pages,
-                                                       page, expected);
-               if (res < 0)
-                       goto mark_errored;
 
-               goto out;
+               i++;
        }
 
+       pages = i;
+
        /*
         * Create a "page actor" which will kmap and kunmap the
         * page cache pages appropriately within the decompressor
         */
-       actor = squashfs_page_actor_init_special(msblk, page, pages, 0);
+       actor = squashfs_page_actor_init_special(msblk, page, pages, expected);
        if (actor == NULL)
                goto out;
 
@@ -102,12 +84,12 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
                goto mark_errored;
        }
 
-       /* Last page may have trailing bytes not filled */
+       /* Last page (if present) may have trailing bytes not filled */
        bytes = res % PAGE_SIZE;
-       if (bytes) {
-               pageaddr = kmap_atomic(page[pages - 1]);
+       if (page[pages - 1]->index == end_index && bytes) {
+               pageaddr = kmap_local_page(page[pages - 1]);
                memset(pageaddr + bytes, 0, PAGE_SIZE - bytes);
-               kunmap_atomic(pageaddr);
+               kunmap_local(pageaddr);
        }
 
        /* Mark pages as uptodate, unlock and release */
@@ -140,36 +122,3 @@ out:
        kfree(page);
        return res;
 }
-
-
-static int squashfs_read_cache(struct page *target_page, u64 block, int bsize,
-       int pages, struct page **page, int bytes)
-{
-       struct inode *i = target_page->mapping->host;
-       struct squashfs_cache_entry *buffer = squashfs_get_datablock(i->i_sb,
-                                                block, bsize);
-       int res = buffer->error, n, offset = 0;
-
-       if (res) {
-               ERROR("Unable to read page, block %llx, size %x\n", block,
-                       bsize);
-               goto out;
-       }
-
-       for (n = 0; n < pages && bytes > 0; n++,
-                       bytes -= PAGE_SIZE, offset += PAGE_SIZE) {
-               int avail = min_t(int, bytes, PAGE_SIZE);
-
-               if (page[n] == NULL)
-                       continue;
-
-               squashfs_fill_page(page[n], buffer, offset, avail);
-               unlock_page(page[n]);
-               if (page[n] != target_page)
-                       put_page(page[n]);
-       }
-
-out:
-       squashfs_cache_put(buffer);
-       return res;
-}