static struct kmem_cache *dentry_cache __read_mostly;
+/**
+ * read_seqbegin_or_lock - begin a sequence number check or locking block
+ * lock: sequence lock
+ * seq : sequence number to be checked
+ *
+ * First try it once optimistically without taking the lock. If that fails,
+ * take the lock. The sequence number is also used as a marker for deciding
+ * whether to be a reader (even) or writer (odd).
+ * N.B. seq must be initialized to an even number to begin with.
+ */
+static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
+{
+ if (!(*seq & 1)) { /* Even */
+ *seq = read_seqbegin(lock);
+ rcu_read_lock();
+ } else /* Odd */
+ write_seqlock(lock);
+}
+
+/**
+ * read_seqretry_or_unlock - end a seqretry or lock block & return retry status
+ * lock : sequence lock
+ * seq : sequence number
+ * Return: 1 to retry operation again, 0 to continue
+ */
+static inline int read_seqretry_or_unlock(seqlock_t *lock, int *seq)
+{
+ if (!(*seq & 1)) { /* Even */
+ rcu_read_unlock();
+ if (read_seqretry(lock, *seq)) {
+ (*seq)++; /* Take writer lock */
+ return 1;
+ }
+ } else /* Odd */
+ write_sequnlock(lock);
+ return 0;
+}
+
/*
* This is the single most critical data structure when it comes
* to the dcache: the hashtable for lookups. Somebody should try
return 0;
}
+/**
+ * prepend_name - prepend a pathname in front of current buffer pointer
+ * buffer: buffer pointer
+ * buflen: allocated length of the buffer
+ * name: name string and length qstr structure
+ *
+ * With RCU path tracing, it may race with d_move(). Use ACCESS_ONCE() to
+ * make sure that either the old or the new name pointer and length are
+ * fetched. However, there may be mismatch between length and pointer.
+ * The length cannot be trusted, we need to copy it byte-by-byte until
+ * the length is reached or a null byte is found. It also prepends "/" at
+ * the beginning of the name. The sequence number check at the caller will
+ * retry it again when a d_move() does happen. So any garbage in the buffer
+ * due to mismatched pointer and length will be discarded.
+ */
static int prepend_name(char **buffer, int *buflen, struct qstr *name)
{
- return prepend(buffer, buflen, name->name, name->len);
+ const char *dname = ACCESS_ONCE(name->name);
+ u32 dlen = ACCESS_ONCE(name->len);
+ char *p;
+
+ if (*buflen < dlen + 1)
+ return -ENAMETOOLONG;
+ *buflen -= dlen + 1;
+ p = *buffer -= dlen + 1;
+ *p++ = '/';
+ while (dlen--) {
+ char c = *dname++;
+ if (!c)
+ break;
+ *p++ = c;
+ }
+ return 0;
}
/**
* @buffer: pointer to the end of the buffer
* @buflen: pointer to buffer length
*
- * Caller holds the rename_lock.
+ * The function tries to write out the pathname without taking any lock other
+ * than the RCU read lock to make sure that dentries won't go away. It only
+ * checks the sequence number of the global rename_lock as any change in the
+ * dentry's d_seq will be preceded by changes in the rename_lock sequence
+ * number. If the sequence number had been change, it will restart the whole
+ * pathname back-tracing sequence again. It performs a total of 3 trials of
+ * lockless back-tracing sequences before falling back to take the
+ * rename_lock.
*/
static int prepend_path(const struct path *path,
const struct path *root,
struct dentry *dentry = path->dentry;
struct vfsmount *vfsmnt = path->mnt;
struct mount *mnt = real_mount(vfsmnt);
- bool slash = false;
int error = 0;
+ unsigned seq = 0;
+ char *bptr;
+ int blen;
+restart:
+ bptr = *buffer;
+ blen = *buflen;
+ read_seqbegin_or_lock(&rename_lock, &seq);
while (dentry != root->dentry || vfsmnt != root->mnt) {
struct dentry * parent;
if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
/* Global root? */
- if (!mnt_has_parent(mnt))
- goto global_root;
- dentry = mnt->mnt_mountpoint;
- mnt = mnt->mnt_parent;
- vfsmnt = &mnt->mnt;
- continue;
+ if (mnt_has_parent(mnt)) {
+ dentry = mnt->mnt_mountpoint;
+ mnt = mnt->mnt_parent;
+ vfsmnt = &mnt->mnt;
+ continue;
+ }
+ /*
+ * Filesystems needing to implement special "root names"
+ * should do so with ->d_dname()
+ */
+ if (IS_ROOT(dentry) &&
+ (dentry->d_name.len != 1 ||
+ dentry->d_name.name[0] != '/')) {
+ WARN(1, "Root dentry has weird name <%.*s>\n",
+ (int) dentry->d_name.len,
+ dentry->d_name.name);
+ }
+ if (!error)
+ error = is_mounted(vfsmnt) ? 1 : 2;
+ break;
}
parent = dentry->d_parent;
prefetch(parent);
- spin_lock(&dentry->d_lock);
- error = prepend_name(buffer, buflen, &dentry->d_name);
- spin_unlock(&dentry->d_lock);
- if (!error)
- error = prepend(buffer, buflen, "/", 1);
+ error = prepend_name(&bptr, &blen, &dentry->d_name);
if (error)
break;
- slash = true;
dentry = parent;
}
+ if (read_seqretry_or_unlock(&rename_lock, &seq))
+ goto restart;
- if (!error && !slash)
- error = prepend(buffer, buflen, "/", 1);
-
- return error;
-
-global_root:
- /*
- * Filesystems needing to implement special "root names"
- * should do so with ->d_dname()
- */
- if (IS_ROOT(dentry) &&
- (dentry->d_name.len != 1 || dentry->d_name.name[0] != '/')) {
- WARN(1, "Root dentry has weird name <%.*s>\n",
- (int) dentry->d_name.len, dentry->d_name.name);
- }
- if (!slash)
- error = prepend(buffer, buflen, "/", 1);
- if (!error)
- error = is_mounted(vfsmnt) ? 1 : 2;
+ if (error >= 0 && bptr == *buffer) {
+ if (--blen < 0)
+ error = -ENAMETOOLONG;
+ else
+ *--bptr = '/';
+ }
+ *buffer = bptr;
+ *buflen = blen;
return error;
}
prepend(&res, &buflen, "\0", 1);
br_read_lock(&vfsmount_lock);
- write_seqlock(&rename_lock);
error = prepend_path(path, root, &res, &buflen);
- write_sequnlock(&rename_lock);
br_read_unlock(&vfsmount_lock);
if (error < 0)
prepend(&res, &buflen, "\0", 1);
br_read_lock(&vfsmount_lock);
- write_seqlock(&rename_lock);
error = prepend_path(path, &root, &res, &buflen);
- write_sequnlock(&rename_lock);
br_read_unlock(&vfsmount_lock);
if (error > 1)
get_fs_root(current->fs, &root);
br_read_lock(&vfsmount_lock);
- write_seqlock(&rename_lock);
error = path_with_deleted(path, &root, &res, &buflen);
- write_sequnlock(&rename_lock);
br_read_unlock(&vfsmount_lock);
if (error < 0)
res = ERR_PTR(error);
char *end = buffer + buflen;
/* these dentries are never renamed, so d_lock is not needed */
if (prepend(&end, &buflen, " (deleted)", 11) ||
- prepend_name(&end, &buflen, &dentry->d_name) ||
+ prepend(&end, &buflen, dentry->d_name.name, dentry->d_name.len) ||
prepend(&end, &buflen, "/", 1))
end = ERR_PTR(-ENAMETOOLONG);
- return end;
+ return end;
}
/*
*/
static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
{
- char *end = buf + buflen;
- char *retval;
+ char *end, *retval;
+ int len, seq = 0;
+ int error = 0;
- prepend(&end, &buflen, "\0", 1);
+restart:
+ end = buf + buflen;
+ len = buflen;
+ prepend(&end, &len, "\0", 1);
if (buflen < 1)
goto Elong;
/* Get '/' right */
retval = end-1;
*retval = '/';
-
+ read_seqbegin_or_lock(&rename_lock, &seq);
while (!IS_ROOT(dentry)) {
struct dentry *parent = dentry->d_parent;
int error;
prefetch(parent);
- spin_lock(&dentry->d_lock);
- error = prepend_name(&end, &buflen, &dentry->d_name);
- spin_unlock(&dentry->d_lock);
- if (error != 0 || prepend(&end, &buflen, "/", 1) != 0)
- goto Elong;
+ error = prepend_name(&end, &len, &dentry->d_name);
+ if (error)
+ break;
retval = end;
dentry = parent;
}
+ if (read_seqretry_or_unlock(&rename_lock, &seq))
+ goto restart;
+ if (error)
+ goto Elong;
return retval;
Elong:
return ERR_PTR(-ENAMETOOLONG);
char *dentry_path_raw(struct dentry *dentry, char *buf, int buflen)
{
- char *retval;
-
- write_seqlock(&rename_lock);
- retval = __dentry_path(dentry, buf, buflen);
- write_sequnlock(&rename_lock);
-
- return retval;
+ return __dentry_path(dentry, buf, buflen);
}
EXPORT_SYMBOL(dentry_path_raw);
char *p = NULL;
char *retval;
- write_seqlock(&rename_lock);
if (d_unlinked(dentry)) {
p = buf + buflen;
if (prepend(&p, &buflen, "//deleted", 10) != 0)
buflen++;
}
retval = __dentry_path(dentry, buf, buflen);
- write_sequnlock(&rename_lock);
if (!IS_ERR(retval) && p)
*p = '/'; /* restore '/' overriden with '\0' */
return retval;
error = -ENOENT;
br_read_lock(&vfsmount_lock);
- write_seqlock(&rename_lock);
if (!d_unlinked(pwd.dentry)) {
unsigned long len;
char *cwd = page + PAGE_SIZE;
prepend(&cwd, &buflen, "\0", 1);
error = prepend_path(&pwd, &root, &cwd, &buflen);
- write_sequnlock(&rename_lock);
br_read_unlock(&vfsmount_lock);
if (error < 0)
error = -EFAULT;
}
} else {
- write_sequnlock(&rename_lock);
br_read_unlock(&vfsmount_lock);
}
projects / GitHub / exynos8895 / android_kernel_samsung_universal8895.git / commitdiff