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[PATCH 08/10] teach page_get_link() to work in RCU mode

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From: Al Viro <viro@zeniv.linux.org.uk>

more or less along the lines of Neil's patchset, sans the insanity
around kmap().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/namei.c            | 19 +++++++++++++------
 fs/proc/self.c        |  2 +-
 fs/proc/thread_self.c |  2 +-
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 089c37f..76cc4a2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4534,12 +4534,19 @@ const char *page_get_link(struct dentry *dentry, struct inode *inode,
 	struct page *page;
 	struct address_space *mapping = inode->i_mapping;
 
-	if (!dentry)
-		return ERR_PTR(-ECHILD);
-
-	page = read_mapping_page(mapping, 0, NULL);
-	if (IS_ERR(page))
-		return (char*)page;
+	if (!dentry) {
+		page = find_get_page(mapping, 0);
+		if (!page)
+			return ERR_PTR(-ECHILD);
+		if (!PageUptodate(page)) {
+			put_page(page);
+			return ERR_PTR(-ECHILD);
+		}
+	} else {
+		page = read_mapping_page(mapping, 0, NULL);
+		if (IS_ERR(page))
+			return (char*)page;
+	}
 	*cookie = page;
 	BUG_ON(mapping_gfp_mask(mapping) & __GFP_HIGHMEM);
 	kaddr = page_address(page);
diff --git a/fs/proc/self.c b/fs/proc/self.c
index bc599fb..9dd0ae6 100644
--- a/fs/proc/self.c
+++ b/fs/proc/self.c
@@ -21,7 +21,7 @@ static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
 static const char *proc_self_get_link(struct dentry *dentry,
 				      struct inode *inode, void **cookie)
 {
-	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+	struct pid_namespace *ns = inode->i_sb->s_fs_info;
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	char *name;
 
diff --git a/fs/proc/thread_self.c b/fs/proc/thread_self.c
index 1c78507..50eef6f 100644
--- a/fs/proc/thread_self.c
+++ b/fs/proc/thread_self.c
@@ -22,7 +22,7 @@ static int proc_thread_self_readlink(struct dentry *dentry, char __user *buffer,
 static const char *proc_thread_self_get_link(struct dentry *dentry,
 					     struct inode *inode, void **cookie)
 {
-	struct pid_namespace *ns = dentry->d_sb->s_fs_info;
+	struct pid_namespace *ns = inode->i_sb->s_fs_info;
 	pid_t tgid = task_tgid_nr_ns(current, ns);
 	pid_t pid = task_pid_nr_ns(current, ns);
 	char *name;
-- 
2.1.4

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Thread

[PATCHSET] ->follow_link() without dropping from RCU mode Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:00 +0100
  [PATCH 08/10] teach page_get_link() to work in RCU mode Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 09/10] teach shmem_get_link() to work in RCU mode Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 01/10] switch befs long symlinks to page_symlink_operations Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 10/10] teach proc_self_get_link()/proc_thread_self_get_link() to work in RCU mode Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 06/10] [vfs] don't put symlink bodies in pagecache into highmem Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
    Re: [PATCH 06/10] [vfs] don't put symlink bodies in pagecache into  highmem Dave Chinner <david@fromorbit.com> - 2015-11-20 00:10 +0100
  [PATCH 05/10] namei: page_getlink() and page_follow_link_light() are the same thing Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 03/10] udf: don't duplicate page_symlink_inode_operations Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 04/10] ufs: get rid of ->setattr() for symlinks Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100
  [PATCH 02/10] logfs: don't duplicate page_symlink_inode_operations Al Viro <viro@ZenIV.linux.org.uk> - 2015-11-18 00:10 +0100

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