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From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexander Potapenko <glider@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Andy Lutomirski <luto@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
	Borislav Petkov <bp@alien8.de>, Christoph Hellwig <hch@lst.de>,
	Christoph Lameter <cl@linux.com>,
	David Rientjes <rientjes@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	Eric Dumazet <edumazet@google.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ilya Leoshkevich <iii@linux.ibm.com>,
	Ingo Molnar <mingo@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Kees Cook <keescook@chromium.org>, Marco Elver <elver@google.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Pekka Enberg <penberg@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Petr Mladek <pmladek@suse.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	kasan-dev <kasan-dev@googlegroups.com>,
	Linux-MM <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Evgenii Stepanov <eugenis@google.com>,
	Nathan Chancellor <nathan@kernel.org>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Segher Boessenkool <segher@kernel.crashing.org>,
	Vitaly Buka <vitalybuka@google.com>,
	linux-toolchains <linux-toolchains@vger.kernel.org>
Subject: [PATCH 6/7] lookup_fast(): don't bother with inode
Date: Tue, 5 Jul 2022 00:16:30 +0100	[thread overview]
Message-ID: <YsN0zovcB+d26OcT@ZenIV> (raw)
In-Reply-To: <YsN0GURKuaAqXB/e@ZenIV>

Note that validation of ->d_seq after ->d_inode fetch is gone, along
with fetching of ->d_inode itself.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/namei.c | 24 +++++-------------------
 1 file changed, 5 insertions(+), 19 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index fe95fe39634c..cdb61d09df79 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1617,8 +1617,7 @@ static struct dentry *__lookup_hash(const struct qstr *name,
 	return dentry;
 }
 
-static struct dentry *lookup_fast(struct nameidata *nd,
-				  struct inode **inode)
+static struct dentry *lookup_fast(struct nameidata *nd)
 {
 	struct dentry *dentry, *parent = nd->path.dentry;
 	int status = 1;
@@ -1636,22 +1635,11 @@ static struct dentry *lookup_fast(struct nameidata *nd,
 			return NULL;
 		}
 
-		/*
-		 * This sequence count validates that the inode matches
-		 * the dentry name information from lookup.
-		 */
-		*inode = d_backing_inode(dentry);
-		if (unlikely(read_seqcount_retry(&dentry->d_seq, nd->next_seq)))
-			return ERR_PTR(-ECHILD);
-
-		/*
+	        /*
 		 * This sequence count validates that the parent had no
 		 * changes while we did the lookup of the dentry above.
-		 *
-		 * The memory barrier in read_seqcount_begin of child is
-		 *  enough, we can use __read_seqcount_retry here.
 		 */
-		if (unlikely(__read_seqcount_retry(&parent->d_seq, nd->seq)))
+		if (unlikely(read_seqcount_retry(&parent->d_seq, nd->seq)))
 			return ERR_PTR(-ECHILD);
 
 		status = d_revalidate(dentry, nd->flags);
@@ -1993,7 +1981,6 @@ static const char *handle_dots(struct nameidata *nd, int type)
 static const char *walk_component(struct nameidata *nd, int flags)
 {
 	struct dentry *dentry;
-	struct inode *inode;
 	/*
 	 * "." and ".." are special - ".." especially so because it has
 	 * to be able to know about the current root directory and
@@ -2004,7 +1991,7 @@ static const char *walk_component(struct nameidata *nd, int flags)
 			put_link(nd);
 		return handle_dots(nd, nd->last_type);
 	}
-	dentry = lookup_fast(nd, &inode);
+	dentry = lookup_fast(nd);
 	if (IS_ERR(dentry))
 		return ERR_CAST(dentry);
 	if (unlikely(!dentry)) {
@@ -3392,7 +3379,6 @@ 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;
-	struct inode *inode;
 	struct dentry *dentry;
 	const char *res;
 
@@ -3408,7 +3394,7 @@ static const char *open_last_lookups(struct nameidata *nd,
 		if (nd->last.name[nd->last.len])
 			nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY;
 		/* we _can_ be in RCU mode here */
-		dentry = lookup_fast(nd, &inode);
+		dentry = lookup_fast(nd);
 		if (IS_ERR(dentry))
 			return ERR_CAST(dentry);
 		if (likely(dentry))
-- 
2.30.2


  parent reply	other threads:[~2022-07-04 23:17 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20220701142310.2188015-1-glider@google.com>
2022-07-01 14:23 ` [PATCH v4 43/45] namei: initialize parameters passed to step_into() Alexander Potapenko
2022-07-02 17:23   ` Linus Torvalds
2022-07-03  3:59     ` Al Viro
2022-07-04  2:52     ` Al Viro
2022-07-04  8:20       ` Alexander Potapenko
2022-07-04 13:44         ` Al Viro
2022-07-04 13:55           ` Al Viro
2022-07-04 15:49           ` Alexander Potapenko
2022-07-04 16:03             ` Greg Kroah-Hartman
2022-07-04 16:33               ` Alexander Potapenko
2022-07-04 18:23             ` Segher Boessenkool
2022-07-04 16:00           ` Al Viro
2022-07-04 16:47             ` Alexander Potapenko
2022-07-04 17:36       ` Linus Torvalds
2022-07-04 19:02         ` Al Viro
2022-07-04 19:16           ` Linus Torvalds
2022-07-04 19:55             ` Al Viro
2022-07-04 20:24               ` Linus Torvalds
2022-07-04 20:46                 ` Al Viro
2022-07-04 20:51                   ` Linus Torvalds
2022-07-04 21:04                     ` Al Viro
2022-07-04 23:13                       ` [PATCH 1/7] __follow_mount_rcu(): verify that mount_lock remains unchanged Al Viro
2022-07-04 23:14                         ` [PATCH 2/7] follow_dotdot{,_rcu}(): change calling conventions Al Viro
2022-07-04 23:14                         ` [PATCH 3/7] namei: stash the sampled ->d_seq into nameidata Al Viro
2022-07-04 23:15                         ` [PATCH 4/7] step_into(): lose inode argument Al Viro
2022-07-04 23:15                         ` [PATCH 5/7] follow_dotdot{,_rcu}(): don't bother with inode Al Viro
2022-07-04 23:16                         ` Al Viro [this message]
2022-07-04 23:17                         ` [PATCH 7/7] step_into(): move fetching ->d_inode past handle_mounts() Al Viro
2022-07-04 23:19                         ` [PATCH 1/7] __follow_mount_rcu(): verify that mount_lock remains unchanged Al Viro
2022-07-05  0:06                           ` Linus Torvalds
2022-07-05  3:48                             ` Al Viro
2022-07-04 20:47                 ` [PATCH v4 43/45] namei: initialize parameters passed to step_into() Linus Torvalds
2022-08-08 16:37   ` Alexander Potapenko

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