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Date: Fri, 24 Oct 2008 23:35:45 +0400
From: Alexey Dobriyan <adobriyan@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: [PATCH] proc: stop using BKL
On Fri, Oct 24, 2008 at 11:55:15AM -0400, Christoph Hellwig wrote:
> On Fri, Oct 24, 2008 at 03:46:06PM +0400, Alexey Dobriyan wrote:
> > 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).
> >
> > Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
>
> Once you stop taking BKL in readdir you also need to switch to
> generic_file_llseek for those directories.
Hm, indeed. here is second version:
commit af22e6782098da2da2bd7e7428a7327f821cb157
Author: Alexey Dobriyan <adobriyan@...il.com>
Date: Fri Oct 24 23:32:05 2008 +0400
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: Alexey Dobriyan <adobriyan@...il.com>
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 60a359b..db7fa5c 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -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,
};
diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 2543fd0..3e76bb9 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -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();
}
/*
diff --git a/fs/proc/proc_net.c b/fs/proc/proc_net.c
index 7bc296f..04d1270 100644
--- a/fs/proc/proc_net.c
+++ b/fs/proc/proc_net.c
@@ -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,
};
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 7761602..f6299a2 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -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;
--
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