Remove BKL from remote_llseek v2

- Replace remote_llseek with generic_file_llseek_unlocked (to force compilation
failures in all users)
- Change all users to either use generic_file_llseek_unlocked directly or
take the BKL around. I changed the file systems who don't use the BKL
for anything (CIFS, GFS) to call it directly. NCPFS and SMBFS and NFS
take the BKL, but explicitely in their own source now.

I moved them all over in a single patch to avoid unbisectable sections.

Open problem: 32bit kernels can corrupt fpos because its modification
is not atomic, but they can do that anyways because there's other paths who
modify it without BKL.

Do we need a special lock for the pos/f_version = 0 checks?

Trond says the NFS BKL is likely not needed, but keep it for now
until his full audit.

v2: Use generic_file_llseek_unlocked instead of remote_llseek_unlocked
    and factor duplicated code (suggested by hch)

Cc: Trond.Myklebust@netapp.com
Cc: swhiteho@redhat.com
Cc: sfrench@samba.org
Cc: vandrove@vc.cvut.cz

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

7 files changed, 42 insertions, 34 deletions

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index 427a7c695896..aeff0fe5b6b9 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -581,7 +581,7 @@ static loff_t cifs_llseek(struct file *file, loff_t offset, int origin)
                 if (retval < 0)
                         return (loff_t)retval;
         }
-        return remote_llseek(file, offset, origin);
+        return generic_file_llseek_unlocked(file, offset, origin);
 }
 
 struct file_system_type cifs_fs_type = {
diff --git a/fs/gfs2/ops_file.c b/fs/gfs2/ops_file.c
index e1b7d525a066..24dd59450088 100644
--- a/fs/gfs2/ops_file.c
+++ b/fs/gfs2/ops_file.c
@@ -62,11 +62,11 @@ static loff_t gfs2_llseek(struct file *file, loff_t offset, int origin)
                 error = gfs2_glock_nq_init(ip->i_gl, LM_ST_SHARED, LM_FLAG_ANY,
                                            &i_gh);
                 if (!error) {
-                        error = remote_llseek(file, offset, origin);
+                        error = generic_file_llseek_unlocked(file, offset, origin);
                         gfs2_glock_dq_uninit(&i_gh);
                 }
         } else
-                error = remote_llseek(file, offset, origin);
+                error = generic_file_llseek_unlocked(file, offset, origin);
 
         return error;
 }
diff --git a/fs/ncpfs/file.c b/fs/ncpfs/file.c
index 2b145de45b39..6a7d901f1936 100644
--- a/fs/ncpfs/file.c
+++ b/fs/ncpfs/file.c
@@ -18,6 +18,7 @@
 #include <linux/slab.h>
 #include <linux/vmalloc.h>
 #include <linux/sched.h>
+#include <linux/smp_lock.h>
 
 #include <linux/ncp_fs.h>
 #include "ncplib_kernel.h"
@@ -281,9 +282,18 @@ static int ncp_release(struct inode *inode, struct file *file) {
         return 0;
 }
 
+static loff_t ncp_remote_llseek(struct file *file, loff_t offset, int origin)
+{
+        loff_t ret;
+        lock_kernel();
+        ret = generic_file_llseek_unlocked(file, offset, origin);
+        unlock_kernel();
+        return ret;
+}
+
 const struct file_operations ncp_file_operations =
 {
-        .llseek         = remote_llseek,
+        .llseek         = ncp_remote_llseek,
         .read           = ncp_file_read,
         .write          = ncp_file_write,
         .ioctl          = ncp_ioctl,
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 3536b01164f9..a34eb78989f5 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -170,6 +170,7 @@ force_reval:
 
 static loff_t nfs_file_llseek(struct file *filp, loff_t offset, int origin)
 {
+        loff_t loff;
         /* origin == SEEK_END => we must revalidate the cached file length */
         if (origin == SEEK_END) {
                 struct inode *inode = filp->f_mapping->host;
@@ -177,7 +178,10 @@ static loff_t nfs_file_llseek(struct file *filp, loff_t offset, int origin)
                 if (retval < 0)
                         return (loff_t)retval;
         }
-        return remote_llseek(filp, offset, origin);
+        lock_kernel();  /* BKL needed? */
+        loff = generic_file_llseek_unlocked(filp, offset, origin);
+        unlock_kernel();
+        return loff;
 }
 
 /*
diff --git a/fs/read_write.c b/fs/read_write.c
index f0d1240a5c69..9ba495d5a29b 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -31,12 +31,12 @@ const struct file_operations generic_ro_fops = {
 
 EXPORT_SYMBOL(generic_ro_fops);
 
-loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
+loff_t
+generic_file_llseek_unlocked(struct file *file, loff_t offset, int origin)
 {
         loff_t retval;
         struct inode *inode = file->f_mapping->host;
 
-        mutex_lock(&inode->i_mutex);
         switch (origin) {
                 case SEEK_END:
                         offset += inode->i_size;
@@ -46,42 +46,26 @@ loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
         }
         retval = -EINVAL;
         if (offset>=0 && offset<=inode->i_sb->s_maxbytes) {
+                /* Special lock needed here? */
                 if (offset != file->f_pos) {
                         file->f_pos = offset;
                         file->f_version = 0;
                 }
                 retval = offset;
         }
-        mutex_unlock(&inode->i_mutex);
         return retval;
 }
+EXPORT_SYMBOL(generic_file_llseek_unlocked);
 
-EXPORT_SYMBOL(generic_file_llseek);
-
-loff_t remote_llseek(struct file *file, loff_t offset, int origin)
+loff_t generic_file_llseek(struct file *file, loff_t offset, int origin)
 {
-        loff_t retval;
-
-        lock_kernel();
-        switch (origin) {
-                case SEEK_END:
-                        offset += i_size_read(file->f_path.dentry->d_inode);
-                        break;
-                case SEEK_CUR:
-                        offset += file->f_pos;
-        }
-        retval = -EINVAL;
-        if (offset>=0 && offset<=file->f_path.dentry->d_inode->i_sb->s_maxbytes) {
-                if (offset != file->f_pos) {
-                        file->f_pos = offset;
-                        file->f_version = 0;
-                }
-                retval = offset;
-        }
-        unlock_kernel();
-        return retval;
+        loff_t n;
+        mutex_lock(&file->f_dentry->d_inode->i_mutex);
+        n = generic_file_llseek_unlocked(file, offset, origin);
+        mutex_unlock(&file->f_dentry->d_inode->i_mutex);
+        return n;
 }
-EXPORT_SYMBOL(remote_llseek);
+EXPORT_SYMBOL(generic_file_llseek);
 
 loff_t no_llseek(struct file *file, loff_t offset, int origin)
 {
diff --git a/fs/smbfs/file.c b/fs/smbfs/file.c
index efbe29af3d7a..2294783320cb 100644
--- a/fs/smbfs/file.c
+++ b/fs/smbfs/file.c
@@ -422,9 +422,18 @@ smb_file_permission(struct inode *inode, int mask, struct nameidata *nd)
         return error;
 }
 
+static loff_t smb_remote_llseek(struct file *file, loff_t offset, int origin)
+{
+        loff_t ret;
+        lock_kernel();
+        ret = generic_file_llseek_unlocked(file, offset, origin);
+        unlock_kernel();
+        return ret;
+}
+
 const struct file_operations smb_file_operations =
 {
-        .llseek         = remote_llseek,
+        .llseek         = smb_remote_llseek,
         .read           = do_sync_read,
         .aio_read       = smb_file_aio_read,
         .write          = do_sync_write,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f413085f748e..b158e5161bca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1871,7 +1871,8 @@ extern void
 file_ra_state_init(struct file_ra_state *ra, struct address_space *mapping);
 extern loff_t no_llseek(struct file *file, loff_t offset, int origin);
 extern loff_t generic_file_llseek(struct file *file, loff_t offset, int origin);
-extern loff_t remote_llseek(struct file *file, loff_t offset, int origin);
+extern loff_t generic_file_llseek_unlocked(struct file *file, loff_t offset,
+                        int origin);
 extern int generic_file_open(struct inode * inode, struct file * filp);
 extern int nonseekable_open(struct inode * inode, struct file * filp);