Commit b4df2b92 authored by Alexey Dobriyan's avatar Alexey Dobriyan
Browse files

proc: stop using BKL 



There are four BKL users in proc: de_put(), proc_lookup_de(),
proc_readdir_de(), proc_root_readdir(),

1) de_put()
-----------
de_put() is classic atomic_dec_and_test() refcount wrapper -- no BKL
needed. BKL doesn't matter to possible refcount leak as well.

2) proc_lookup_de()
-------------------
Walking PDE list is protected by proc_subdir_lock(), proc_get_inode() is
potentially blocking, all callers of proc_lookup_de() eventually end up
from ->lookup hooks which is protected by directory's ->i_mutex -- BKL
doesn't protect anything.

3) proc_readdir_de()
--------------------
"." and ".." part doesn't need BKL, walking PDE list is under
proc_subdir_lock, calling filldir callback is potentially blocking
because it writes to luserspace. All proc_readdir_de() callers
eventually come from ->readdir hook which is under directory's
->i_mutex -- BKL doesn't protect anything.

4) proc_root_readdir_de()
-------------------------
proc_root_readdir_de is ->readdir hook, see (3).

Since readdir hooks doesn't use BKL anymore, switch to
generic_file_llseek, since it also takes directory's i_mutex.

Signed-off-by: default avatarAlexey Dobriyan <adobriyan@gmail.com>
parent fe0bdec6

fs/proc/generic.c

+2 −6
Original line number Diff line number Diff line
@@ -14,7 +14,6 @@ 
#include <linux/stat.h>

#include <linux/module.h>

#include <linux/mount.h>

#include <linux/smp_lock.h>

#include <linux/init.h>

#include <linux/idr.h>

#include <linux/namei.h>
@@ -379,7 +378,6 @@ struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir, 
	struct inode *inode = NULL;

	int error = -ENOENT;



	lock_kernel();

	spin_lock(&proc_subdir_lock);

	for (de = de->subdir; de ; de = de->next) {

		if (de->namelen != dentry->d_name.len)
@@ -397,7 +395,6 @@ struct dentry *proc_lookup_de(struct proc_dir_entry *de, struct inode *dir, 
	}

	spin_unlock(&proc_subdir_lock);

out_unlock:

	unlock_kernel();



	if (inode) {

		dentry->d_op = &proc_dentry_operations;
@@ -432,8 +429,6 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent, 
	struct inode *inode = filp->f_path.dentry->d_inode;

	int ret = 0;



	lock_kernel();



	ino = inode->i_ino;

	i = filp->f_pos;

	switch (i) {
@@ -487,7 +482,7 @@ int proc_readdir_de(struct proc_dir_entry *de, struct file *filp, void *dirent, 
			spin_unlock(&proc_subdir_lock);

	}

	ret = 1;

out:	unlock_kernel();

out:

	return ret;	

}
@@ -504,6 +499,7 @@ int proc_readdir(struct file *filp, void *dirent, filldir_t filldir) 
 * the /proc directory.

 */

static const struct file_operations proc_dir_operations = {

	.llseek			= generic_file_llseek,

	.read			= generic_read_dir,

	.readdir		= proc_readdir,

};

fs/proc/inode.c

+0 −3
Original line number Diff line number Diff line
@@ -35,16 +35,13 @@ struct proc_dir_entry *de_get(struct proc_dir_entry *de) 
 */

void de_put(struct proc_dir_entry *de)

{

	lock_kernel();

	if (!atomic_read(&de->count)) {

		printk("de_put: entry %s already free!\n", de->name);

		unlock_kernel();

		return;

	}



	if (atomic_dec_and_test(&de->count))

		free_proc_entry(de);

	unlock_kernel();

}



/*

fs/proc/proc_net.c

+1 −1
Original line number Diff line number Diff line
@@ -18,7 +18,6 @@ 
#include <linux/sched.h>

#include <linux/module.h>

#include <linux/bitops.h>

#include <linux/smp_lock.h>

#include <linux/mount.h>

#include <linux/nsproxy.h>

#include <net/net_namespace.h>
@@ -172,6 +171,7 @@ static int proc_tgid_net_readdir(struct file *filp, void *dirent, 
}



const struct file_operations proc_net_operations = {

	.llseek		= generic_file_llseek,

	.read		= generic_read_dir,

	.readdir	= proc_tgid_net_readdir,

};

fs/proc/root.c

+1 −7
Original line number Diff line number Diff line
@@ -16,7 +16,6 @@ 
#include <linux/sched.h>

#include <linux/module.h>

#include <linux/bitops.h>

#include <linux/smp_lock.h>

#include <linux/mount.h>

#include <linux/pid_namespace.h>
@@ -162,17 +161,12 @@ static int proc_root_readdir(struct file * filp, 
	unsigned int nr = filp->f_pos;

	int ret;



	lock_kernel();



	if (nr < FIRST_PROCESS_ENTRY) {

		int error = proc_readdir(filp, dirent, filldir);

		if (error <= 0) {

			unlock_kernel();

		if (error <= 0)

			return error;

		}

		filp->f_pos = FIRST_PROCESS_ENTRY;

	}

	unlock_kernel();



	ret = proc_pid_readdir(filp, dirent, filldir);

	return ret;

CRA Git | Maintained and supported by SUSTech CRA and CCSE