RE: [PATCH 13/14] d_path: prepend_path() is unlikely to return non-zero

Justin He
2021-06-25T08:01:21Z

Hi Al

> -----Original Message-----
> From: Al Viro <viro@ftp.linux.org.uk> On Behalf Of Al Viro
> Sent: Wednesday, May 19, 2021 8:49 AM
> To: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Justin He <Justin.He@arm.com>; Petr Mladek <pmladek@suse.com>; Steven
> Rostedt <rostedt@goodmis.org>; Sergey Senozhatsky
> <senozhatsky@chromium.org>; Andy Shevchenko
> <andriy.shevchenko@linux.intel.com>; Rasmus Villemoes
> <linux@rasmusvillemoes.dk>; Jonathan Corbet <corbet@lwn.net>; Heiko
> Carstens <hca@linux.ibm.com>; Vasily Gorbik <gor@linux.ibm.com>; Christian
> Borntraeger <borntraeger@de.ibm.com>; Eric W . Biederman
> <ebiederm@xmission.com>; Darrick J. Wong <darrick.wong@oracle.com>; Peter
> Zijlstra (Intel) <peterz@infradead.org>; Ira Weiny <ira.weiny@intel.com>;
> Eric Biggers <ebiggers@google.com>; Ahmed S. Darwish
> <a.darwish@linutronix.de>; open list:DOCUMENTATION <linux-
> doc@vger.kernel.org>; Linux Kernel Mailing List <linux-
> kernel@vger.kernel.org>; linux-s390 <linux-s390@vger.kernel.org>; linux-
> fsdevel <linux-fsdevel@vger.kernel.org>
> Subject: [PATCH 13/14] d_path: prepend_path() is unlikely to return non-
> zero
>
> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
> ---
> fs/d_path.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/d_path.c b/fs/d_path.c
> index ba629879a4bf..8a9cd44f6689 100644
> --- a/fs/d_path.c
> +++ b/fs/d_path.c
> @@ -187,7 +187,7 @@ char *__d_path(const struct path *path,
> DECLARE_BUFFER(b, buf, buflen);
>
> prepend(&b, "", 1);
> - if (prepend_path(path, root, &b) > 0)
> + if (unlikely(prepend_path(path, root, &b) > 0))
> return NULL;
> return extract_string(&b);
> }
> @@ -199,7 +199,7 @@ char *d_absolute_path(const struct path *path,
> DECLARE_BUFFER(b, buf, buflen);
>
> prepend(&b, "", 1);
> - if (prepend_path(path, &root, &b) > 1)
> + if (unlikely(prepend_path(path, &root, &b) > 1))
> return ERR_PTR(-EINVAL);
> return extract_string(&b);
> }
> @@ -396,7 +396,7 @@ SYSCALL_DEFINE2(getcwd, char __user *, buf, unsigned
> long, size)
> DECLARE_BUFFER(b, page, PATH_MAX);
>
> prepend(&b, "", 1);
> - if (prepend_path(&pwd, &root, &b) > 0)
> + if (unlikely(prepend_path(&pwd, &root, &b) > 0))
> prepend(&b, "(unreachable)", 13);
> rcu_read_unlock();
>
> --
> 2.11.0
I tested it with a debugging patch as follows:
diff --git a/fs/d_path.c b/fs/d_path.c
index aea254ac9e1f..8eecd04be7bb 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c
@@ -210,6 +210,7 @@ static int prepend_path(const struct path *path,
b = *p;
read_seqbegin_or_lock(&rename_lock, &seq);
error = __prepend_path(path->dentry, real_mount(path->mnt), root, &b);
+ printk("prepend=%d",error);
if (!(seq & 1))
rcu_read_unlock();
if (need_seqretry(&rename_lock, seq)) {

Then the result seems a little different:
root@entos-ampere-02:~# dmesg |grep prepend=1 |wc -l
7417
root@entos-ampere-02:~# dmesg |grep prepend=0 |wc -l
772

The kernel is 5.13.0-rc2+ + this series + my '%pD' series

Any thoughts?

---
Cheers,
Jia He (Justin)

IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.