fs: symlink write_begin allocation context fix

With the write_begin/write_end aops, page_symlink was broken because it
could no longer pass a GFP_NOFS type mask into the point where the
allocations happened.  They are done in write_begin, which would always
assume that the filesystem can be entered from reclaim.  This bug could
cause filesystem deadlocks.

The funny thing with having a gfp_t mask there is that it doesn't really
allow the caller to arbitrarily tinker with the context in which it can be
called.  It couldn't ever be GFP_ATOMIC, for example, because it needs to
take the page lock.  The only thing any callers care about is __GFP_FS
anyway, so turn that into a single flag.

Add a new flag for write_begin, AOP_FLAG_NOFS.  Filesystems can now act on
this flag in their write_begin function.  Change __grab_cache_page to
accept a nofs argument as well, to honour that flag (while we're there,
change the name to grab_cache_page_write_begin which is more instructive
and does away with random leading underscores).

This is really a more flexible way to go in the end anyway -- if a
filesystem happens to want any extra allocations aside from the pagecache
ones in ints write_begin function, it may now use GFP_KERNEL (rather than
GFP_NOFS) for common case allocations (eg.  ocfs2_alloc_write_ctxt, for a
random example).

[kosaki.motohiro@jp.fujitsu.com: fix ubifs]
[kosaki.motohiro@jp.fujitsu.com: fix fuse]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: <stable@kernel.org>		[2.6.28.x]
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Cleaned up the calling convention: just pass in the AOP flags
  untouched to the grab_cache_page_write_begin() function.  That
  just simplifies everybody, and may even allow future expansion of the
  logic.   - Linus ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

22 files changed, 49 insertions, 36 deletions

diff --git a/fs/affs/file.c b/fs/affs/file.c
index 1377b1240b6e..9246cb4aa018 100644
--- a/fs/affs/file.c
+++ b/fs/affs/file.c
@@ -628,7 +628,7 @@ static int affs_write_begin_ofs(struct file *file, struct address_space *mapping
         }
 
         index = pos >> PAGE_CACHE_SHIFT;
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/afs/write.c b/fs/afs/write.c
index d6b85dab35fc..3fb36d433621 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -144,7 +144,7 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
         candidate->state = AFS_WBACK_PENDING;
         init_waitqueue_head(&candidate->waitq);
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page) {
                 kfree(candidate);
                 return -ENOMEM;
diff --git a/fs/buffer.c b/fs/buffer.c
index 776ae091d3b0..a13f09b696f7 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1996,7 +1996,7 @@ int block_write_begin(struct file *file, struct address_space *mapping,
         page = *pagep;
         if (page == NULL) {
                 ownpage = 1;
-                page = __grab_cache_page(mapping, index);
+                page = grab_cache_page_write_begin(mapping, index, flags);
                 if (!page) {
                         status = -ENOMEM;
                         goto out;
@@ -2502,7 +2502,7 @@ int nobh_write_begin(struct file *file, struct address_space *mapping,
         from = pos & (PAGE_CACHE_SIZE - 1);
         to = from + len;
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index b1e1fc6a6e6a..12bb656fbe75 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2074,7 +2074,7 @@ static int cifs_write_begin(struct file *file, struct address_space *mapping,
 
         cFYI(1, ("write_begin from %lld len %d", (long long)pos, len));
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page) {
                 rc = -ENOMEM;
                 goto out;
diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index 04d7b3fa1ac6..46cec2b69796 100644
--- a/fs/ecryptfs/mmap.c
+++ b/fs/ecryptfs/mmap.c
@@ -288,7 +288,7 @@ static int ecryptfs_write_begin(struct file *file,
         loff_t prev_page_end_size;
         int rc = 0;
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/ext3/inode.c b/fs/ext3/inode.c
index c4bdccf976b5..5fa453b49a64 100644
--- a/fs/ext3/inode.c
+++ b/fs/ext3/inode.c
@@ -1161,7 +1161,7 @@ static int ext3_write_begin(struct file *file, struct address_space *mapping,
         to = from + len;
 
 retry:
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/ext3/namei.c b/fs/ext3/namei.c
index 297ea8dfac7c..1dd2abe6313e 100644
--- a/fs/ext3/namei.c
+++ b/fs/ext3/namei.c
@@ -2175,8 +2175,7 @@ retry:
                  * We have a transaction open.  All is sweetness.  It also sets
                  * i_size in generic_commit_write().
                  */
-                err = __page_symlink(inode, symname, l,
-                                mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS);
+                err = __page_symlink(inode, symname, l, 1);
                 if (err) {
                         drop_nlink(inode);
                         unlock_new_inode(inode);
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 7c3325e0b005..6702a49992a6 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1346,7 +1346,7 @@ retry:
                 goto out;
         }
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page) {
                 ext4_journal_stop(handle);
                 ret = -ENOMEM;
@@ -2550,7 +2550,7 @@ retry:
                 goto out;
         }
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page) {
                 ext4_journal_stop(handle);
                 ret = -ENOMEM;
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index da98a9012fa5..9fd2a5e1be4d 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -2212,8 +2212,7 @@ retry:
                  * We have a transaction open.  All is sweetness.  It also sets
                  * i_size in generic_commit_write().
                  */
-                err = __page_symlink(inode, symname, l,
-                                mapping_gfp_mask(inode->i_mapping) & ~__GFP_FS);
+                err = __page_symlink(inode, symname, l, 1);
                 if (err) {
                         clear_nlink(inode);
                         unlock_new_inode(inode);
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 34930a964b82..4c9ee7011265 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -646,7 +646,7 @@ static int fuse_write_begin(struct file *file, struct address_space *mapping,
 {
         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 
-        *pagep = __grab_cache_page(mapping, index);
+        *pagep = grab_cache_page_write_begin(mapping, index, flags);
         if (!*pagep)
                 return -ENOMEM;
         return 0;
@@ -779,7 +779,7 @@ static ssize_t fuse_fill_write_pages(struct fuse_req *req,
                         break;
 
                 err = -ENOMEM;
-                page = __grab_cache_page(mapping, index);
+                page = grab_cache_page_write_begin(mapping, index, 0);
                 if (!page)
                         break;
 
diff --git a/fs/gfs2/ops_address.c b/fs/gfs2/ops_address.c
index 27563816e1c5..15f710f2d4da 100644
--- a/fs/gfs2/ops_address.c
+++ b/fs/gfs2/ops_address.c
@@ -675,7 +675,7 @@ static int gfs2_write_begin(struct file *file, struct address_space *mapping,
                 goto out_trans_fail;
 
         error = -ENOMEM;
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         *pagep = page;
         if (unlikely(!page))
                 goto out_endtrans;
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 3a31451ac170..5c538e0ec14b 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -501,7 +501,7 @@ int hostfs_write_begin(struct file *file, struct address_space *mapping,
 {
         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
 
-        *pagep = __grab_cache_page(mapping, index);
+        *pagep = grab_cache_page_write_begin(mapping, index, flags);
         if (!*pagep)
                 return -ENOMEM;
         return 0;
diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
index 5a98aa87c853..5edc2bf20581 100644
--- a/fs/jffs2/file.c
+++ b/fs/jffs2/file.c
@@ -132,7 +132,7 @@ static int jffs2_write_begin(struct file *filp, struct address_space *mapping,
         uint32_t pageofs = index << PAGE_CACHE_SHIFT;
         int ret = 0;
 
-        pg = __grab_cache_page(mapping, index);
+        pg = grab_cache_page_write_begin(mapping, index, flags);
         if (!pg)
                 return -ENOMEM;
         *pagep = pg;
diff --git a/fs/libfs.c b/fs/libfs.c
index e960a8321902..bdaec17fa388 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -360,7 +360,7 @@ int simple_write_begin(struct file *file, struct address_space *mapping,
         index = pos >> PAGE_CACHE_SHIFT;
         from = pos & (PAGE_CACHE_SIZE - 1);
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
 
diff --git a/fs/namei.c b/fs/namei.c
index dd5c9f0bf829..df2d3df4f049 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2817,18 +2817,23 @@ void page_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
         }
 }
 
-int __page_symlink(struct inode *inode, const char *symname, int len,
-                gfp_t gfp_mask)
+/*
+ * The nofs argument instructs pagecache_write_begin to pass AOP_FLAG_NOFS
+ */
+int __page_symlink(struct inode *inode, const char *symname, int len, int nofs)
 {
         struct address_space *mapping = inode->i_mapping;
         struct page *page;
         void *fsdata;
         int err;
         char *kaddr;
+        unsigned int flags = AOP_FLAG_UNINTERRUPTIBLE;
+        if (nofs)
+                flags |= AOP_FLAG_NOFS;
 
 retry:
         err = pagecache_write_begin(NULL, mapping, 0, len-1,
-                                AOP_FLAG_UNINTERRUPTIBLE, &page, &fsdata);
+                                flags, &page, &fsdata);
         if (err)
                 goto fail;
 
@@ -2852,7 +2857,7 @@ fail:
 int page_symlink(struct inode *inode, const char *symname, int len)
 {
         return __page_symlink(inode, symname, len,
-                        mapping_gfp_mask(inode->i_mapping));
+                        !(mapping_gfp_mask(inode->i_mapping) & __GFP_FS));
 }
 
 const struct inode_operations page_symlink_inode_operations = {
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index d319b49f8f06..90f292b520d2 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -354,7 +354,7 @@ static int nfs_write_begin(struct file *file, struct address_space *mapping,
                 file->f_path.dentry->d_name.name,
                 mapping->host->i_ino, len, (long long) pos);
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/reiserfs/inode.c b/fs/reiserfs/inode.c
index 145c2d3e5e01..ed04f47007f8 100644
--- a/fs/reiserfs/inode.c
+++ b/fs/reiserfs/inode.c
@@ -2561,7 +2561,7 @@ static int reiserfs_write_begin(struct file *file,
         }
 
         index = pos >> PAGE_CACHE_SHIFT;
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (!page)
                 return -ENOMEM;
         *pagep = page;
diff --git a/fs/smbfs/file.c b/fs/smbfs/file.c
index e4f8d51a5553..92d5e8ffb639 100644
--- a/fs/smbfs/file.c
+++ b/fs/smbfs/file.c
@@ -297,7 +297,7 @@ static int smb_write_begin(struct file *file, struct address_space *mapping,
                         struct page **pagep, void **fsdata)
 {
         pgoff_t index = pos >> PAGE_CACHE_SHIFT;
-        *pagep = __grab_cache_page(mapping, index);
+        *pagep = grab_cache_page_write_begin(mapping, index, flags);
         if (!*pagep)
                 return -ENOMEM;
         return 0;
diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
index fe82d2464d46..bf37374567fa 100644
--- a/fs/ubifs/file.c
+++ b/fs/ubifs/file.c
@@ -219,7 +219,8 @@ static void release_existing_page_budget(struct ubifs_info *c)
 }
 
 static int write_begin_slow(struct address_space *mapping,
-                            loff_t pos, unsigned len, struct page **pagep)
+                            loff_t pos, unsigned len, struct page **pagep,
+                            unsigned flags)
 {
         struct inode *inode = mapping->host;
         struct ubifs_info *c = inode->i_sb->s_fs_info;
@@ -247,7 +248,7 @@ static int write_begin_slow(struct address_space *mapping,
         if (unlikely(err))
                 return err;
 
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (unlikely(!page)) {
                 ubifs_release_budget(c, &req);
                 return -ENOMEM;
@@ -438,7 +439,7 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
                 return -EROFS;
 
         /* Try out the fast-path part first */
-        page = __grab_cache_page(mapping, index);
+        page = grab_cache_page_write_begin(mapping, index, flags);
         if (unlikely(!page))
                 return -ENOMEM;
 
@@ -483,7 +484,7 @@ static int ubifs_write_begin(struct file *file, struct address_space *mapping,
                 unlock_page(page);
                 page_cache_release(page);
 
-                return write_begin_slow(mapping, pos, len, pagep);
+                return write_begin_slow(mapping, pos, len, pagep, flags);
         }
 
         /*
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e2170ee21e18..f2a3010140e3 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -423,6 +423,9 @@ enum positive_aop_returns {
 
 #define AOP_FLAG_UNINTERRUPTIBLE        0x0001 /* will not do a short write */
 #define AOP_FLAG_CONT_EXPAND            0x0002 /* called from cont_expand */
+#define AOP_FLAG_NOFS                   0x0004 /* used by filesystem to direct
+                                                * helper code (eg buffer layer)
+                                                * to clear GFP_FS from alloc */
 
 /*
  * oh the beauties of C type declarations.
@@ -2035,7 +2038,7 @@ extern int page_readlink(struct dentry *, char __user *, int);
 extern void *page_follow_link_light(struct dentry *, struct nameidata *);
 extern void page_put_link(struct dentry *, struct nameidata *, void *);
 extern int __page_symlink(struct inode *inode, const char *symname, int len,
-                gfp_t gfp_mask);
+                int nofs);
 extern int page_symlink(struct inode *inode, const char *symname, int len);
 extern const struct inode_operations page_symlink_inode_operations;
 extern int generic_readlink(struct dentry *, char __user *, int);
diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 709742be02f0..01ca0856caff 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -241,7 +241,8 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
 unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
                         int tag, unsigned int nr_pages, struct page **pages);
 
-struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index);
+struct page *grab_cache_page_write_begin(struct address_space *mapping,
+                        pgoff_t index, unsigned flags);
 
 /*
  * Returns locked page at given index in given cache, creating it if needed.
diff --git a/mm/filemap.c b/mm/filemap.c
index f3e5f8944d17..f8c69273c37f 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2140,19 +2140,24 @@ EXPORT_SYMBOL(generic_file_direct_write);
  * Find or create a page at the given pagecache position. Return the locked
  * page. This function is specifically for buffered writes.
  */
-struct page *__grab_cache_page(struct address_space *mapping, pgoff_t index)
+struct page *grab_cache_page_write_begin(struct address_space *mapping,
+                                        pgoff_t index, unsigned flags)
 {
         int status;
         struct page *page;
+        gfp_t gfp_notmask = 0;
+        if (flags & AOP_FLAG_NOFS)
+                gfp_notmask = __GFP_FS;
 repeat:
         page = find_lock_page(mapping, index);
         if (likely(page))
                 return page;
 
-        page = page_cache_alloc(mapping);
+        page = __page_cache_alloc(mapping_gfp_mask(mapping) & ~gfp_notmask);
         if (!page)
                 return NULL;
-        status = add_to_page_cache_lru(page, mapping, index, GFP_KERNEL);
+        status = add_to_page_cache_lru(page, mapping, index,
+                                                GFP_KERNEL & ~gfp_notmask);
         if (unlikely(status)) {
                 page_cache_release(page);
                 if (status == -EEXIST)
@@ -2161,7 +2166,7 @@ repeat:
         }
         return page;
 }
-EXPORT_SYMBOL(__grab_cache_page);
+EXPORT_SYMBOL(grab_cache_page_write_begin);
 
 static ssize_t generic_perform_write(struct file *file,
                                 struct iov_iter *i, loff_t pos)