[PATCH 4/5] fs: honor LOOKUP_NONBLOCK for the last part of file open

[Jens Axboe <axboe@xxxxxxxxx>]

We handle it for the path resolution itself, but we should also factor
it in for open_last_lookups() and tmpfile open.

We don't allow RESOLVE_NONBLOCK with O_TRUNC, so that case we can safely
ignore.

Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
 fs/namei.c | 39 +++++++++++++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 07a1aa874f65..1f976a213eef 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3127,6 +3127,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 	struct dentry *dir = nd->path.dentry;
 	int open_flag = op->open_flag;
 	bool got_write = false;
+	bool nonblock = nd->flags & LOOKUP_NONBLOCK;
 	unsigned seq;
 	struct inode *inode;
 	struct dentry *dentry;
@@ -3164,17 +3165,38 @@ static const char *open_last_lookups(struct nameidata *nd,
 	}
 
 	if (open_flag & (O_CREAT | O_TRUNC | O_WRONLY | O_RDWR)) {
-		got_write = !mnt_want_write(nd->path.mnt);
+		if (nonblock) {
+			got_write = !mnt_want_write_trylock(nd->path.mnt);
+			if (!got_write)
+				return ERR_PTR(-EAGAIN);
+		} else {
+			got_write = !mnt_want_write(nd->path.mnt);
+		}
 		/*
 		 * do _not_ fail yet - we might not need that or fail with
 		 * a different error; let lookup_open() decide; we'll be
 		 * dropping this one anyway.
 		 */
 	}
-	if (open_flag & O_CREAT)
-		inode_lock(dir->d_inode);
-	else
-		inode_lock_shared(dir->d_inode);
+	if (open_flag & O_CREAT) {
+		if (nonblock) {
+			if (!inode_trylock(dir->d_inode)) {
+				dentry = ERR_PTR(-EAGAIN);
+				goto drop_write;
+			}
+		} else {
+			inode_lock(dir->d_inode);
+		}
+	} else {
+		if (nonblock) {
+			if (!inode_trylock_shared(dir->d_inode)) {
+				dentry = ERR_PTR(-EAGAIN);
+				goto drop_write;
+			}
+		} else {
+			inode_lock_shared(dir->d_inode);
+		}
+	}
 	dentry = lookup_open(nd, file, op, got_write);
 	if (!IS_ERR(dentry) && (file->f_mode & FMODE_CREATED))
 		fsnotify_create(dir->d_inode, dentry);
@@ -3183,6 +3205,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 	else
 		inode_unlock_shared(dir->d_inode);
 
+drop_write:
 	if (got_write)
 		mnt_drop_write(nd->path.mnt);
 
@@ -3242,6 +3265,7 @@ static int do_open(struct nameidata *nd,
 		open_flag &= ~O_TRUNC;
 		acc_mode = 0;
 	} else if (d_is_reg(nd->path.dentry) && open_flag & O_TRUNC) {
+		WARN_ON_ONCE(nd->flags & LOOKUP_NONBLOCK);
 		error = mnt_want_write(nd->path.mnt);
 		if (error)
 			return error;
@@ -3311,7 +3335,10 @@ static int do_tmpfile(struct nameidata *nd, unsigned flags,
 	int error = path_lookupat(nd, flags | LOOKUP_DIRECTORY, &path);
 	if (unlikely(error))
 		return error;
-	error = mnt_want_write(path.mnt);
+	if (flags & LOOKUP_NONBLOCK)
+		error = mnt_want_write_trylock(path.mnt);
+	else
+		error = mnt_want_write(path.mnt);
 	if (unlikely(error))
 		goto out;
 	child = vfs_tmpfile(path.dentry, op->mode, op->open_flag);
-- 
2.29.2