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vfs: make d_path() get the root path under RCU 

This avoids the spinlocks and refcounts in the d_path() sequence too
(used by /proc and various other entities).  See commit 8b19e34188 for
the equivalent getcwd() system call path.

And unlike getcwd(), d_path() doesn't copy the result to user space, so
I don't need to fear _that_ particular bug happening again.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2013-09-12 13:24:55 -07:00
parent 3272c544da
commit 68f0d9d92e
1 changed files with 14 additions and 2 deletions
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16
fs/dcache.c
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@ -2869,6 +2869,16 @@ static int prepend_unreachable(char **buffer, int *buflen)
return prepend(buffer, buflen, "(unreachable)", 13);
}
static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)
{
unsigned seq;
do {
seq = read_seqcount_begin(&fs->seq);
*root = fs->root;
} while (read_seqcount_retry(&fs->seq, seq));
}
/**
* d_path - return the path of a dentry
* @path: path to report
@ -2901,13 +2911,15 @@ char *d_path(const struct path *path, char *buf, int buflen)
if (path->dentry->d_op && path->dentry->d_op->d_dname)
return path->dentry->d_op->d_dname(path->dentry, buf, buflen);
get_fs_root(current->fs, &root);
rcu_read_lock();
get_fs_root_rcu(current->fs, &root);
br_read_lock(&vfsmount_lock);
error = path_with_deleted(path, &root, &res, &buflen);
br_read_unlock(&vfsmount_lock);
rcu_read_unlock();
if (error < 0)
res = ERR_PTR(error);
path_put(&root);
return res;
}
EXPORT_SYMBOL(d_path);