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Date: Fri, 03 Jul 2009 11:18:19 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Pekka Enberg <penberg@...helsinki.fi>, Ingo Molnar <mingo@...e.hu>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
git-commits-head@...r.kernel.org
Subject: Re: Exiting with locks still held (was Re: [PATCH] kmemleak: Fix
scheduling-while-atomic bug)
On Thu, 2009-07-02 at 10:39 -0700, Linus Torvalds wrote:
> On Thu, 2 Jul 2009, Catalin Marinas wrote:
> >
> > Initially, the scan_mutex was acquired in kmemleak_open() and released
> > in kmemleak_release() (corresponding to /sys/kernel/debug/kmemleak
> > operations). This was causing some lockdep reports when the file was
> > closed from a different task than the one opening it. This patch moves
> > the scan_mutex acquiring in kmemleak_write() or kmemleak_seq_show().
>
> This is better, but not really how you are supposed to do it.
>
> The whole seq-file thing is very much _designed_ for taking a lock at the
> beginning of the operation, and releasing it at the end. It's a very
> common pattern.
Thanks for this. Here's the updated patch (the difference from misc.c is
that it uses mutex_lock_interruptible):
kmemleak: Do not acquire scan_mutex in kmemleak_open()
From: Catalin Marinas <catalin.marinas@....com>
Initially, the scan_mutex was acquired in kmemleak_open() and released
in kmemleak_release() (corresponding to /sys/kernel/debug/kmemleak
operations). This was causing some lockdep reports when the file was
closed from a different task than the one opening it. This patch moves
the scan_mutex acquiring in kmemleak_write() or kmemleak_seq_start()
with releasing in kmemleak_seq_stop().
Signed-off-by: Catalin Marinas <catalin.marinas@....com>
---
mm/kmemleak.c | 63 +++++++++++++++++++++++++++------------------------------
1 files changed, 30 insertions(+), 33 deletions(-)
diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index 23bf5f0..c6e0aae 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -1103,6 +1103,11 @@ static void *kmemleak_seq_start(struct seq_file *seq, loff_t *pos)
{
struct kmemleak_object *object;
loff_t n = *pos;
+ int err;
+
+ err = mutex_lock_interruptible(&scan_mutex);
+ if (err < 0)
+ return ERR_PTR(err);
rcu_read_lock();
list_for_each_entry_rcu(object, &object_list, object_list) {
@@ -1146,8 +1151,15 @@ static void *kmemleak_seq_next(struct seq_file *seq, void *v, loff_t *pos)
*/
static void kmemleak_seq_stop(struct seq_file *seq, void *v)
{
- if (v)
- put_object(v);
+ if (!IS_ERR(v)) {
+ /*
+ * kmemleak_seq_start may return ERR_PTR if the scan_mutex
+ * waiting was interrupted, so only release it if !IS_ERR.
+ */
+ mutex_unlock(&scan_mutex);
+ if (v)
+ put_object(v);
+ }
}
/*
@@ -1174,36 +1186,15 @@ static const struct seq_operations kmemleak_seq_ops = {
static int kmemleak_open(struct inode *inode, struct file *file)
{
- int ret = 0;
-
if (!atomic_read(&kmemleak_enabled))
return -EBUSY;
- ret = mutex_lock_interruptible(&scan_mutex);
- if (ret < 0)
- goto out;
- if (file->f_mode & FMODE_READ) {
- ret = seq_open(file, &kmemleak_seq_ops);
- if (ret < 0)
- goto scan_unlock;
- }
- return ret;
-
-scan_unlock:
- mutex_unlock(&scan_mutex);
-out:
- return ret;
+ return seq_open(file, &kmemleak_seq_ops);
}
static int kmemleak_release(struct inode *inode, struct file *file)
{
- int ret = 0;
-
- if (file->f_mode & FMODE_READ)
- seq_release(inode, file);
- mutex_unlock(&scan_mutex);
-
- return ret;
+ return seq_release(inode, file);
}
/*
@@ -1223,15 +1214,17 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
{
char buf[64];
int buf_size;
-
- if (!atomic_read(&kmemleak_enabled))
- return -EBUSY;
+ int ret;
buf_size = min(size, (sizeof(buf) - 1));
if (strncpy_from_user(buf, user_buf, buf_size) < 0)
return -EFAULT;
buf[buf_size] = 0;
+ ret = mutex_lock_interruptible(&scan_mutex);
+ if (ret < 0)
+ return ret;
+
if (strncmp(buf, "off", 3) == 0)
kmemleak_disable();
else if (strncmp(buf, "stack=on", 8) == 0)
@@ -1244,11 +1237,10 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
stop_scan_thread();
else if (strncmp(buf, "scan=", 5) == 0) {
unsigned long secs;
- int err;
- err = strict_strtoul(buf + 5, 0, &secs);
- if (err < 0)
- return err;
+ ret = strict_strtoul(buf + 5, 0, &secs);
+ if (ret < 0)
+ goto out;
stop_scan_thread();
if (secs) {
jiffies_scan_wait = msecs_to_jiffies(secs * 1000);
@@ -1257,7 +1249,12 @@ static ssize_t kmemleak_write(struct file *file, const char __user *user_buf,
} else if (strncmp(buf, "scan", 4) == 0)
kmemleak_scan();
else
- return -EINVAL;
+ ret = -EINVAL;
+
+out:
+ mutex_unlock(&scan_mutex);
+ if (ret < 0)
+ return ret;
/* ignore the rest of the buffer, only one command at a time */
*ppos += size;
--
Catalin
--
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