lkml.org 
[lkml]   [2018]   [Dec]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] squashfs: enable __GFP_FS in ->readpage to prevent hang in mem alloc
Date
There is no need to disable __GFP_FS in ->readpage:
* It's a read-only fs, so there will be no dirty/writeback page and
there will be no deadlock against the caller's locked page
* It just allocates one page, so compaction will not be invoked
* It doesn't take any inode lock, so the reclamation of inode will be fine

And no __GFP_FS may lead to hang in __alloc_pages_slowpath() if a
squashfs page fault occurs in the context of a memory hogger, because
the hogger will not be killed due to the logic in __alloc_pages_may_oom().

Signed-off-by: Hou Tao <houtao1@huawei.com>
---
fs/squashfs/file.c | 3 ++-
fs/squashfs/file_direct.c | 4 +++-
fs/squashfs/squashfs_fs_f.h | 25 +++++++++++++++++++++++++
3 files changed, 30 insertions(+), 2 deletions(-)
create mode 100644 fs/squashfs/squashfs_fs_f.h

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index f1c1430ae721..8603dda4a719 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -51,6 +51,7 @@
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
+#include "squashfs_fs_f.h"
#include "squashfs.h"

/*
@@ -414,7 +415,7 @@ void squashfs_copy_cache(struct page *page, struct squashfs_cache_entry *buffer,
TRACE("bytes %d, i %d, available_bytes %d\n", bytes, i, avail);

push_page = (i == page->index) ? page :
- grab_cache_page_nowait(page->mapping, i);
+ squashfs_grab_cache_page_nowait(page->mapping, i);

if (!push_page)
continue;
diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
index 80db1b86a27c..a0fdd6215348 100644
--- a/fs/squashfs/file_direct.c
+++ b/fs/squashfs/file_direct.c
@@ -17,6 +17,7 @@
#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs_fs_i.h"
+#include "squashfs_fs_f.h"
#include "squashfs.h"
#include "page_actor.h"

@@ -60,7 +61,8 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
/* Try to grab all the pages covered by the Squashfs block */
for (missing_pages = 0, i = 0, n = start_index; i < pages; i++, n++) {
page[i] = (n == target_page->index) ? target_page :
- grab_cache_page_nowait(target_page->mapping, n);
+ squashfs_grab_cache_page_nowait(
+ target_page->mapping, n);

if (page[i] == NULL) {
missing_pages++;
diff --git a/fs/squashfs/squashfs_fs_f.h b/fs/squashfs/squashfs_fs_f.h
new file mode 100644
index 000000000000..fc5fb7aeb27d
--- /dev/null
+++ b/fs/squashfs/squashfs_fs_f.h
@@ -0,0 +1,25 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef SQUASHFS_FS_F
+#define SQUASHFS_FS_F
+
+/*
+ * No need to use FGP_NOFS here:
+ * 1. It's a read-only fs, so there will be no dirty/writeback page and
+ * there will be no deadlock against the caller's locked page.
+ * 2. It just allocates one page, so compaction will not be invoked.
+ * 3. It doesn't take any inode lock, so the reclamation of inode
+ * will be fine.
+ *
+ * And GFP_NOFS may lead to infinite loop in __alloc_pages_slowpath() if a
+ * squashfs page fault occurs in the context of a memory hogger, because
+ * the hogger will not be killed due to the logic in __alloc_pages_may_oom().
+ */
+static inline struct page *
+squashfs_grab_cache_page_nowait(struct address_space *mapping, pgoff_t index)
+{
+ return pagecache_get_page(mapping, index,
+ FGP_LOCK|FGP_CREAT|FGP_NOWAIT,
+ mapping_gfp_mask(mapping));
+}
+#endif
+
--
2.16.2.dirty
\
 
 \ /
  Last update: 2018-12-04 03:07    [W:0.097 / U:14.388 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site