Coda: add spin lock to protect accesses to struct coda_inode_info.

We mostly need it to protect cached user permissions. The c_flags field
is advisory, reading the wrong value is harmless and in the worst case
we hit a slow path where we have to make an extra upcall to the
userspace cache manager when revalidating a dentry or inode.

Signed-off-by: Yoshihisa Abe <yoshiabe@cs.cmu.edu>
Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

7 files changed, 58 insertions, 17 deletions

diff --git a/fs/coda/cache.c b/fs/coda/cache.c
index a5bf5771a22a..9060f08e70cf 100644
--- a/fs/coda/cache.c
+++ b/fs/coda/cache.c
@@ -17,6 +17,7 @@
 #include <linux/string.h>
 #include <linux/list.h>
 #include <linux/sched.h>
+#include <linux/spinlock.h>
 
 #include <linux/coda.h>
 #include <linux/coda_linux.h>
@@ -31,19 +32,23 @@ void coda_cache_enter(struct inode *inode, int mask)
 {
         struct coda_inode_info *cii = ITOC(inode);
 
+        spin_lock(&cii->c_lock);
         cii->c_cached_epoch = atomic_read(&permission_epoch);
         if (cii->c_uid != current_fsuid()) {
                 cii->c_uid = current_fsuid();
                 cii->c_cached_perm = mask;
         } else
                 cii->c_cached_perm |= mask;
+        spin_unlock(&cii->c_lock);
 }
 
 /* remove cached acl from an inode */
 void coda_cache_clear_inode(struct inode *inode)
 {
         struct coda_inode_info *cii = ITOC(inode);
+        spin_lock(&cii->c_lock);
         cii->c_cached_epoch = atomic_read(&permission_epoch) - 1;
+        spin_unlock(&cii->c_lock);
 }
 
 /* remove all acl caches */
@@ -57,13 +62,15 @@ void coda_cache_clear_all(struct super_block *sb)
 int coda_cache_check(struct inode *inode, int mask)
 {
         struct coda_inode_info *cii = ITOC(inode);
-        int hit;
+        int hit;
         
-        hit = (mask & cii->c_cached_perm) == mask &&
-                cii->c_uid == current_fsuid() &&
-                cii->c_cached_epoch == atomic_read(&permission_epoch);
+        spin_lock(&cii->c_lock);
+        hit = (mask & cii->c_cached_perm) == mask &&
+            cii->c_uid == current_fsuid() &&
+            cii->c_cached_epoch == atomic_read(&permission_epoch);
+        spin_unlock(&cii->c_lock);
 
-        return hit;
+        return hit;
 }
 
 
diff --git a/fs/coda/cnode.c b/fs/coda/cnode.c
index a7a780929eec..602240569c89 100644
--- a/fs/coda/cnode.c
+++ b/fs/coda/cnode.c
@@ -45,13 +45,15 @@ static void coda_fill_inode(struct inode *inode, struct coda_vattr *attr)
 static int coda_test_inode(struct inode *inode, void *data)
 {
         struct CodaFid *fid = (struct CodaFid *)data;
-        return coda_fideq(&(ITOC(inode)->c_fid), fid);
+        struct coda_inode_info *cii = ITOC(inode);
+        return coda_fideq(&cii->c_fid, fid);
 }
 
 static int coda_set_inode(struct inode *inode, void *data)
 {
         struct CodaFid *fid = (struct CodaFid *)data;
-        ITOC(inode)->c_fid = *fid;
+        struct coda_inode_info *cii = ITOC(inode);
+        cii->c_fid = *fid;
         return 0;
 }
 
@@ -71,6 +73,7 @@ struct inode * coda_iget(struct super_block * sb, struct CodaFid * fid,
                 cii = ITOC(inode);
                 /* we still need to set i_ino for things like stat(2) */
                 inode->i_ino = hash;
+                /* inode is locked and unique, no need to grab cii->c_lock */
                 cii->c_mapcount = 0;
                 unlock_new_inode(inode);
         }
@@ -107,14 +110,20 @@ int coda_cnode_make(struct inode **inode, struct CodaFid *fid, struct super_bloc
 }
 
 
+/* Although we treat Coda file identifiers as immutable, there is one
+ * special case for files created during a disconnection where they may
+ * not be globally unique. When an identifier collision is detected we
+ * first try to flush the cached inode from the kernel and finally
+ * resort to renaming/rehashing in-place. Userspace remembers both old
+ * and new values of the identifier to handle any in-flight upcalls.
+ * The real solution is to use globally unique UUIDs as identifiers, but
+ * retrofitting the existing userspace code for this is non-trivial. */
 void coda_replace_fid(struct inode *inode, struct CodaFid *oldfid, 
                       struct CodaFid *newfid)
 {
-        struct coda_inode_info *cii;
+        struct coda_inode_info *cii = ITOC(inode);
         unsigned long hash = coda_f2i(newfid);
         
-        cii = ITOC(inode);
-
         BUG_ON(!coda_fideq(&cii->c_fid, oldfid));
 
         /* replace fid and rehash inode */
diff --git a/fs/coda/dir.c b/fs/coda/dir.c
index ccd98b0f2b0b..69fbbea75f1b 100644
--- a/fs/coda/dir.c
+++ b/fs/coda/dir.c
@@ -18,6 +18,7 @@
 #include <linux/errno.h>
 #include <linux/string.h>
 #include <linux/smp_lock.h>
+#include <linux/spinlock.h>
 
 #include <asm/uaccess.h>
 
@@ -617,7 +618,9 @@ static int coda_dentry_revalidate(struct dentry *de, struct nameidata *nd)
                 goto out;
 
         /* clear the flags. */
+        spin_lock(&cii->c_lock);
         cii->c_flags &= ~(C_VATTR | C_PURGE | C_FLUSH);
+        spin_unlock(&cii->c_lock);
 
 bad:
         unlock_kernel();
@@ -691,7 +694,10 @@ int coda_revalidate_inode(struct dentry *dentry)
                         goto return_bad;
                 
                 coda_flag_inode_children(inode, C_FLUSH);
+
+                spin_lock(&cii->c_lock);
                 cii->c_flags &= ~(C_VATTR | C_PURGE | C_FLUSH);
+                spin_unlock(&cii->c_lock);
         }
 
 ok:
diff --git a/fs/coda/file.c b/fs/coda/file.c
index ad3cd2abeeb4..c4e395781d41 100644
--- a/fs/coda/file.c
+++ b/fs/coda/file.c
@@ -16,6 +16,7 @@
 #include <linux/cred.h>
 #include <linux/errno.h>
 #include <linux/smp_lock.h>
+#include <linux/spinlock.h>
 #include <linux/string.h>
 #include <linux/slab.h>
 #include <asm/uaccess.h>
@@ -109,19 +110,24 @@ coda_file_mmap(struct file *coda_file, struct vm_area_struct *vma)
 
         coda_inode = coda_file->f_path.dentry->d_inode;
         host_inode = host_file->f_path.dentry->d_inode;
+
+        cii = ITOC(coda_inode);
+        spin_lock(&cii->c_lock);
         coda_file->f_mapping = host_file->f_mapping;
         if (coda_inode->i_mapping == &coda_inode->i_data)
                 coda_inode->i_mapping = host_inode->i_mapping;
 
         /* only allow additional mmaps as long as userspace isn't changing
          * the container file on us! */
-        else if (coda_inode->i_mapping != host_inode->i_mapping)
+        else if (coda_inode->i_mapping != host_inode->i_mapping) {
+                spin_unlock(&cii->c_lock);
                 return -EBUSY;
+        }
 
         /* keep track of how often the coda_inode/host_file has been mmapped */
-        cii = ITOC(coda_inode);
         cii->c_mapcount++;
         cfi->cfi_mapcount++;
+        spin_unlock(&cii->c_lock);
 
         return host_file->f_op->mmap(host_file, vma);
 }
@@ -185,11 +191,13 @@ int coda_release(struct inode *coda_inode, struct file *coda_file)
         cii = ITOC(coda_inode);
 
         /* did we mmap this file? */
+        spin_lock(&cii->c_lock);
         if (coda_inode->i_mapping == &host_inode->i_data) {
                 cii->c_mapcount -= cfi->cfi_mapcount;
                 if (!cii->c_mapcount)
                         coda_inode->i_mapping = &coda_inode->i_data;
         }
+        spin_unlock(&cii->c_lock);
 
         fput(cfi->cfi_container);
         kfree(coda_file->private_data);
diff --git a/fs/coda/inode.c b/fs/coda/inode.c
index bfe8179b1295..0553f3bd7b1b 100644
--- a/fs/coda/inode.c
+++ b/fs/coda/inode.c
@@ -16,6 +16,7 @@
 #include <linux/errno.h>
 #include <linux/unistd.h>
 #include <linux/smp_lock.h>
+#include <linux/spinlock.h>
 #include <linux/file.h>
 #include <linux/vfs.h>
 #include <linux/slab.h>
@@ -51,6 +52,7 @@ static struct inode *coda_alloc_inode(struct super_block *sb)
         ei->c_flags = 0;
         ei->c_uid = 0;
         ei->c_cached_perm = 0;
+        spin_lock_init(&ei->c_lock);
         return &ei->vfs_inode;
 }
 
diff --git a/include/linux/coda_fs_i.h b/include/linux/coda_fs_i.h
index b3ef0c461578..e35071b1de0e 100644
--- a/include/linux/coda_fs_i.h
+++ b/include/linux/coda_fs_i.h
@@ -10,19 +10,24 @@
 
 #include <linux/types.h>
 #include <linux/list.h>
+#include <linux/spinlock.h>
 #include <linux/coda.h>
 
 /*
  * coda fs inode data
+ * c_lock protects accesses to c_flags, c_mapcount, c_cached_epoch, c_uid and
+ * c_cached_perm.
+ * vfs_inode is set only when the inode is created and never changes.
+ * c_fid is set when the inode is created and should be considered immutable.
  */
 struct coda_inode_info {
-        struct CodaFid     c_fid;       /* Coda identifier */
-        u_short            c_flags;     /* flags (see below) */
-        struct list_head   c_cilist;    /* list of all coda inodes */
+        struct CodaFid     c_fid;       /* Coda identifier */
+        u_short            c_flags;     /* flags (see below) */
         unsigned int       c_mapcount;  /* nr of times this inode is mapped */
         unsigned int       c_cached_epoch; /* epoch for cached permissions */
         vuid_t             c_uid;       /* fsuid for cached permissions */
-        unsigned int       c_cached_perm; /* cached access permissions */
+        unsigned int       c_cached_perm; /* cached access permissions */
+        spinlock_t         c_lock;
         struct inode       vfs_inode;
 };
 
diff --git a/include/linux/coda_linux.h b/include/linux/coda_linux.h
index dcc228aa335a..2e914d0771b9 100644
--- a/include/linux/coda_linux.h
+++ b/include/linux/coda_linux.h
@@ -89,7 +89,11 @@ static __inline__ char *coda_i2s(struct inode *inode)
 /* this will not zap the inode away */
 static __inline__ void coda_flag_inode(struct inode *inode, int flag)
 {
-        ITOC(inode)->c_flags |= flag;
+        struct coda_inode_info *cii = ITOC(inode);
+
+        spin_lock(&cii->c_lock);
+        cii->c_flags |= flag;
+        spin_unlock(&cii->c_lock);
 }               
 
 #endif