linux-ext4 - [PATCH 10/11] vfs: trylock inode->i_rwsem in iterate

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Date:   Sun, 27 Aug 2023 21:28:34 +0800
From:   Hao Xu <hao.xu@...ux.dev>
To:     io-uring@...r.kernel.org, Jens Axboe <axboe@...nel.dk>
Cc:     Dominique Martinet <asmadeus@...ewreck.org>,
        Pavel Begunkov <asml.silence@...il.com>,
        Christian Brauner <brauner@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Stefan Roesch <shr@...com>, Clay Harris <bugs@...ycon.org>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-cachefs@...hat.com,
        ecryptfs@...r.kernel.org, linux-nfs@...r.kernel.org,
        linux-unionfs@...r.kernel.org, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-btrfs@...r.kernel.org, codalist@...a.cs.cmu.edu,
        linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
        linux-mm@...ck.org, linux-nilfs@...r.kernel.org,
        devel@...ts.orangefs.org, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, linux-mtd@...ts.infradead.org,
        Wanpeng Li <wanpengli@...cent.com>
Subject: [PATCH 10/11] vfs: trylock inode->i_rwsem in iterate_dir() to support nowait

From: Hao Xu <howeyxu@...cent.com>

Trylock inode->i_rwsem in iterate_dir() to support nowait semantics and
error out -EAGAIN when there is contention.

Signed-off-by: Hao Xu <howeyxu@...cent.com>
---
 fs/readdir.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/readdir.c b/fs/readdir.c
index 6469f076ba6e..664ecd9665a1 100644
--- a/fs/readdir.c
+++ b/fs/readdir.c
@@ -43,6 +43,8 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 	struct inode *inode = file_inode(file);
 	bool shared = false;
 	int res = -ENOTDIR;
+	bool nowait;
+
 	if (file->f_op->iterate_shared)
 		shared = true;
 	else if (!file->f_op->iterate)
@@ -52,16 +54,22 @@ int iterate_dir(struct file *file, struct dir_context *ctx)
 	if (res)
 		goto out;
 
-	if (shared)
-		res = down_read_killable(&inode->i_rwsem);
-	else
-		res = down_write_killable(&inode->i_rwsem);
-	if (res)
+	nowait = ctx->flags & DIR_CONTEXT_F_NOWAIT;
+	if (nowait) {
+		res = shared ? down_read_trylock(&inode->i_rwsem) :
+			       down_write_trylock(&inode->i_rwsem);
+		if (!res)
+			res = -EAGAIN;
+	} else {
+		res = shared ? down_read_killable(&inode->i_rwsem) :
+			       down_write_killable(&inode->i_rwsem);
+	}
+	if (res < 0)
 		goto out;
 
 	res = -ENOENT;
 	if (!IS_DEADDIR(inode)) {
-		res = file_accessed(file, ctx->flags & DIR_CONTEXT_F_NOWAIT);
+		res = file_accessed(file, nowait);
 		if (res == -EAGAIN)
 			goto out_unlock;
 
-- 
2.25.1