From: ebiederm@xmission.com (Eric W. Biederman)
To: Stephen Brennan <stephen.s.brennan@oracle.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
linux-security-module@vger.kernel.org,
Paul Moore <paul@paul-moore.com>,
Stephen Smalley <stephen.smalley.work@gmail.com>,
Eric Paris <eparis@parisplace.org>,
selinux@vger.kernel.org, Casey Schaufler <casey@schaufler-ca.com>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Matthew Wilcox <willy@infradead.org>
Subject: Re: [PATCH v2] proc: Allow pid_revalidate() during LOOKUP_RCU
Date: Sun, 13 Dec 2020 08:30:40 -0600 [thread overview]
Message-ID: <87tusplqwf.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20201204000212.773032-1-stephen.s.brennan@oracle.com> (Stephen Brennan's message of "Thu, 3 Dec 2020 16:02:12 -0800")
Stephen Brennan <stephen.s.brennan@oracle.com> writes:
> The pid_revalidate() function requires dropping from RCU into REF lookup
> mode. When many threads are resolving paths within /proc in parallel,
> this can result in heavy spinlock contention as each thread tries to
> grab a reference to the /proc dentry lock (and drop it shortly
> thereafter).
I am feeling dense at the moment. Which lock specifically are you
referring to? The only locks I can thinking of are sleeping locks,
not spinlocks.
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index ebea9501afb8..833d55a59e20 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1830,19 +1846,22 @@ static int pid_revalidate(struct dentry *dentry, unsigned int flags)
> {
> struct inode *inode;
> struct task_struct *task;
> + int rv = 0;
>
> - if (flags & LOOKUP_RCU)
> - return -ECHILD;
> -
> - inode = d_inode(dentry);
> - task = get_proc_task(inode);
> -
> - if (task) {
> - pid_update_inode(task, inode);
> - put_task_struct(task);
> - return 1;
> + if (flags & LOOKUP_RCU) {
Why do we need to test flags here at all?
Why can't the code simply take an rcu_read_lock unconditionally and just
pass flags into do_pid_update_inode?
> + inode = d_inode_rcu(dentry);
> + task = pid_task(proc_pid(inode), PIDTYPE_PID);
> + if (task)
> + rv = do_pid_update_inode(task, inode, flags);
> + } else {
> + inode = d_inode(dentry);
> + task = get_proc_task(inode);
> + if (task) {
> + rv = do_pid_update_inode(task, inode, flags);
> + put_task_struct(task);
> + }
> }
> - return 0;
> + return rv;
> }
>
> static inline bool proc_inode_is_dead(struct inode *inode)
Eric
next prev parent reply other threads:[~2020-12-13 14:32 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-04 0:02 [PATCH v2] proc: Allow pid_revalidate() during LOOKUP_RCU Stephen Brennan
2020-12-12 20:55 ` Matthew Wilcox
2020-12-13 14:22 ` Eric W. Biederman
2020-12-13 16:29 ` Matthew Wilcox
2020-12-13 23:00 ` Paul Moore
2020-12-15 18:09 ` Casey Schaufler
2020-12-15 22:04 ` Eric W. Biederman
2020-12-15 22:53 ` Casey Schaufler
2020-12-16 1:05 ` Stephen Brennan
2020-12-14 18:45 ` Casey Schaufler
2020-12-14 18:15 ` Stephen Brennan
2020-12-13 14:30 ` Eric W. Biederman [this message]
2020-12-13 16:32 ` Matthew Wilcox
2020-12-14 17:19 ` Stephen Brennan
2020-12-15 21:45 ` Eric W. Biederman
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