[PATCH 0/2] blktrace: fix one kind of lockdep warning

[PATCH 0/2] blktrace: fix one kind of lockdep warning

[Ming Lei]

Hello,

This patchset kills one big kind of lockdep warning by cutting
dependency between q->debugfs_lock and mm->mmap_lock around copy_to_user()
and copy_from_user(().


Ming Lei (2):
  blktrace: don't centralize grabbing q->debugfs_mutex in
    blk_trace_ioctl
  blktrace: move copy_[to|from]_user() out of ->debugfs_lock

 kernel/trace/blktrace.c | 34 ++++++++++++----------------------
 1 file changed, 12 insertions(+), 22 deletions(-)

-- 
2.47.0

[PATCH 1/2] blktrace: don't centralize grabbing q->debugfs_mutex in blk_trace_ioctl

[Ming Lei]

Call each handler directly and the handler do grab q->debugfs_mutex,
prepare for killing dependency between ->debug_mutex and ->mmap_lock.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 kernel/trace/blktrace.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index 8fd292d34d89..f01aae3a2f7b 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -732,34 +732,32 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
 	int ret, start = 0;
 	char b[BDEVNAME_SIZE];
 
-	mutex_lock(&q->debugfs_mutex);
-
 	switch (cmd) {
 	case BLKTRACESETUP:
 		snprintf(b, sizeof(b), "%pg", bdev);
-		ret = __blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
+		ret = blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
 		break;
 #if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
 	case BLKTRACESETUP32:
 		snprintf(b, sizeof(b), "%pg", bdev);
+		mutex_lock(&q->debugfs_mutex);
 		ret = compat_blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
+		mutex_unlock(&q->debugfs_mutex);
 		break;
 #endif
 	case BLKTRACESTART:
 		start = 1;
 		fallthrough;
 	case BLKTRACESTOP:
-		ret = __blk_trace_startstop(q, start);
+		ret = blk_trace_startstop(q, start);
 		break;
 	case BLKTRACETEARDOWN:
-		ret = __blk_trace_remove(q);
+		ret = blk_trace_remove(q);
 		break;
 	default:
 		ret = -ENOTTY;
 		break;
 	}
-
-	mutex_unlock(&q->debugfs_mutex);
 	return ret;
 }
 
-- 
2.47.0

[PATCH 2/2] blktrace: move copy_[to|from]_user() out of ->debugfs_lock

[Ming Lei]

Move copy_[to|from]_user() out of ->debugfs_lock and cut the dependency
between mm->mmap_lock and q->debugfs_lock, then we avoids lots of
lockdep false positive warning. Obviously ->debug_lock isn't needed
for copy_[to|from]_user().

The only behavior change is to call blk_trace_remove() in case of setup
failure handling by re-grabbing ->debugfs_lock, and this way is just
fine since we do cover concurrent setup() & remove().

Reported-by: syzbot+91585b36b538053343e4@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-block/67450fd4.050a0220.1286eb.0007.GAE@google.com/
Closes: https://lore.kernel.org/linux-block/6742e584.050a0220.1cc393.0038.GAE@google.com/
Closes: https://lore.kernel.org/linux-block/6742a600.050a0220.1cc393.002e.GAE@google.com/
Closes: https://lore.kernel.org/linux-block/67420102.050a0220.1cc393.0019.GAE@google.com/
Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 kernel/trace/blktrace.c | 26 +++++++++-----------------
 1 file changed, 9 insertions(+), 17 deletions(-)

diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
index f01aae3a2f7b..18c81e6aa496 100644
--- a/kernel/trace/blktrace.c
+++ b/kernel/trace/blktrace.c
@@ -617,8 +617,9 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	return ret;
 }
 
-static int __blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
-			     struct block_device *bdev, char __user *arg)
+int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
+		    struct block_device *bdev,
+		    char __user *arg)
 {
 	struct blk_user_trace_setup buts;
 	int ret;
@@ -627,26 +628,17 @@ static int __blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
 	if (ret)
 		return -EFAULT;
 
+	mutex_lock(&q->debugfs_mutex);
 	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
+	mutex_unlock(&q->debugfs_mutex);
 	if (ret)
 		return ret;
 
 	if (copy_to_user(arg, &buts, sizeof(buts))) {
-		__blk_trace_remove(q);
+		blk_trace_remove(q);
 		return -EFAULT;
 	}
 	return 0;
-}
-
-int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
-		    struct block_device *bdev,
-		    char __user *arg)
-{
-	int ret;
-
-	mutex_lock(&q->debugfs_mutex);
-	ret = __blk_trace_setup(q, name, dev, bdev, arg);
-	mutex_unlock(&q->debugfs_mutex);
 
 	return ret;
 }
@@ -673,12 +665,14 @@ static int compat_blk_trace_setup(struct request_queue *q, char *name,
 		.pid = cbuts.pid,
 	};
 
+	mutex_lock(&q->debugfs_mutex);
 	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
+	mutex_unlock(&q->debugfs_mutex);
 	if (ret)
 		return ret;
 
 	if (copy_to_user(arg, &buts.name, ARRAY_SIZE(buts.name))) {
-		__blk_trace_remove(q);
+		blk_trace_remove(q);
 		return -EFAULT;
 	}
 
@@ -740,9 +734,7 @@ int blk_trace_ioctl(struct block_device *bdev, unsigned cmd, char __user *arg)
 #if defined(CONFIG_COMPAT) && defined(CONFIG_X86_64)
 	case BLKTRACESETUP32:
 		snprintf(b, sizeof(b), "%pg", bdev);
-		mutex_lock(&q->debugfs_mutex);
 		ret = compat_blk_trace_setup(q, b, bdev->bd_dev, bdev, arg);
-		mutex_unlock(&q->debugfs_mutex);
 		break;
 #endif
 	case BLKTRACESTART:
-- 
2.47.0

Re: [PATCH 0/2] blktrace: fix one kind of lockdep warning

[Jens Axboe]

On 11/28/24 5:50 AM, Ming Lei wrote:
> Hello,
> 
> This patchset kills one big kind of lockdep warning by cutting
> dependency between q->debugfs_lock and mm->mmap_lock around copy_to_user()
> and copy_from_user(().

This is almost identical to one I did a month or two ago, but didn't
get to finish. Thanks for getting this done!

-- 
Jens Axboe

Re: [PATCH 0/2] blktrace: fix one kind of lockdep warning

[Jens Axboe]

On Thu, 28 Nov 2024 20:50:25 +0800, Ming Lei wrote:
> This patchset kills one big kind of lockdep warning by cutting
> dependency between q->debugfs_lock and mm->mmap_lock around copy_to_user()
> and copy_from_user(().
> 
> 
> Ming Lei (2):
>   blktrace: don't centralize grabbing q->debugfs_mutex in
>     blk_trace_ioctl
>   blktrace: move copy_[to|from]_user() out of ->debugfs_lock
> 
> [...]

Applied, thanks!

[1/2] blktrace: don't centralize grabbing q->debugfs_mutex in blk_trace_ioctl
      commit: 36a76c9c0f6dc999834ad34d64ff85be0b2923f9
[2/2] blktrace: move copy_[to|from]_user() out of ->debugfs_lock
      commit: 98c00f3a7804ebdaacd80a269910f80179aa4a51

Best regards,
-- 
Jens Axboe

Re: [PATCH 2/2] blktrace: move copy_[to|from]_user() out of ->debugfs_lock

[Kees Bakker]

Op 28-11-2024 om 13:50 schreef Ming Lei:
> Move copy_[to|from]_user() out of ->debugfs_lock and cut the dependency
> between mm->mmap_lock and q->debugfs_lock, then we avoids lots of
> lockdep false positive warning. Obviously ->debug_lock isn't needed
> for copy_[to|from]_user().
>
> The only behavior change is to call blk_trace_remove() in case of setup
> failure handling by re-grabbing ->debugfs_lock, and this way is just
> fine since we do cover concurrent setup() & remove().
>
> Reported-by: syzbot+91585b36b538053343e4@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/linux-block/67450fd4.050a0220.1286eb.0007.GAE@google.com/
> Closes: https://lore.kernel.org/linux-block/6742e584.050a0220.1cc393.0038.GAE@google.com/
> Closes: https://lore.kernel.org/linux-block/6742a600.050a0220.1cc393.002e.GAE@google.com/
> Closes: https://lore.kernel.org/linux-block/67420102.050a0220.1cc393.0019.GAE@google.com/
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>   kernel/trace/blktrace.c | 26 +++++++++-----------------
>   1 file changed, 9 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index f01aae3a2f7b..18c81e6aa496 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -617,8 +617,9 @@ static int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
>   	return ret;
>   }
>   
> -static int __blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> -			     struct block_device *bdev, char __user *arg)
> +int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> +		    struct block_device *bdev,
> +		    char __user *arg)
>   {
>   	struct blk_user_trace_setup buts;
>   	int ret;
> @@ -627,26 +628,17 @@ static int __blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
>   	if (ret)
>   		return -EFAULT;
>   
> +	mutex_lock(&q->debugfs_mutex);
>   	ret = do_blk_trace_setup(q, name, dev, bdev, &buts);
> +	mutex_unlock(&q->debugfs_mutex);
>   	if (ret)
>   		return ret;
>   
>   	if (copy_to_user(arg, &buts, sizeof(buts))) {
> -		__blk_trace_remove(q);
> +		blk_trace_remove(q);
>   		return -EFAULT;
>   	}
>   	return 0;
> -}
> -
> -int blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> -		    struct block_device *bdev,
> -		    char __user *arg)
> -{
> -	int ret;
> -
> -	mutex_lock(&q->debugfs_mutex);
> -	ret = __blk_trace_setup(q, name, dev, bdev, arg);
> -	mutex_unlock(&q->debugfs_mutex);
>   
>   	return ret;
You forgot to delete "return ret;" from function blk_trace_setup()
>   }
> [...]