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Date:   Wed, 13 Feb 2019 11:25:31 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Sahitya Tummala <stummala@...eaurora.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
CC:     <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] f2fs: do not use mutex lock in atomic context

On 2019/2/4 16:06, Sahitya Tummala wrote:
> Fix below warning coming because of using mutex lock in atomic context.
> 
> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:98
> in_atomic(): 1, irqs_disabled(): 0, pid: 585, name: sh
> Preemption disabled at: __radix_tree_preload+0x28/0x130
> Call trace:
>  dump_backtrace+0x0/0x2b4
>  show_stack+0x20/0x28
>  dump_stack+0xa8/0xe0
>  ___might_sleep+0x144/0x194
>  __might_sleep+0x58/0x8c
>  mutex_lock+0x2c/0x48
>  f2fs_trace_pid+0x88/0x14c
>  f2fs_set_node_page_dirty+0xd0/0x184
> 
> Do not use f2fs_radix_tree_insert() to avoid doing cond_resched() with
> spin_lock() acquired.
> 
> Signed-off-by: Sahitya Tummala <stummala@...eaurora.org>
> ---
>  fs/f2fs/trace.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/f2fs/trace.c b/fs/f2fs/trace.c
> index ce2a5eb..d0ab533 100644
> --- a/fs/f2fs/trace.c
> +++ b/fs/f2fs/trace.c
> @@ -14,7 +14,7 @@
>  #include "trace.h"
>  
>  static RADIX_TREE(pids, GFP_ATOMIC);
> -static struct mutex pids_lock;
> +static spinlock_t pids_lock;
>  static struct last_io_info last_io;
>  
>  static inline void __print_last_io(void)
> @@ -58,23 +58,29 @@ void f2fs_trace_pid(struct page *page)
>  
>  	set_page_private(page, (unsigned long)pid);
>  
> +retry:
>  	if (radix_tree_preload(GFP_NOFS))
>  		return;
>  
> -	mutex_lock(&pids_lock);
> +	spin_lock(&pids_lock);
>  	p = radix_tree_lookup(&pids, pid);
>  	if (p == current)
>  		goto out;
>  	if (p)
>  		radix_tree_delete(&pids, pid);
>  
> -	f2fs_radix_tree_insert(&pids, pid, current);
> +	if (radix_tree_insert(&pids, pid, current)) {
> +		spin_unlock(&pids_lock);
> +		radix_tree_preload_end();
> +		cond_resched();
> +		goto retry;
> +	}
>  
>  	trace_printk("%3x:%3x %4x %-16s\n",
>  			MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
>  			pid, current->comm);

Hi Sahitya,

Can trace_printk sleep? For safety, how about moving it out of spinlock?

Thanks,

>  out:
> -	mutex_unlock(&pids_lock);
> +	spin_unlock(&pids_lock);
>  	radix_tree_preload_end();
>  }
>  
> @@ -119,7 +125,7 @@ void f2fs_trace_ios(struct f2fs_io_info *fio, int flush)
>  
>  void f2fs_build_trace_ios(void)
>  {
> -	mutex_init(&pids_lock);
> +	spin_lock_init(&pids_lock);
>  }
>  
>  #define PIDVEC_SIZE	128
> @@ -147,7 +153,7 @@ void f2fs_destroy_trace_ios(void)
>  	pid_t next_pid = 0;
>  	unsigned int found;
>  
> -	mutex_lock(&pids_lock);
> +	spin_lock(&pids_lock);
>  	while ((found = gang_lookup_pids(pid, next_pid, PIDVEC_SIZE))) {
>  		unsigned idx;
>  
> @@ -155,5 +161,5 @@ void f2fs_destroy_trace_ios(void)
>  		for (idx = 0; idx < found; idx++)
>  			radix_tree_delete(&pids, pid[idx]);
>  	}
> -	mutex_unlock(&pids_lock);
> +	spin_unlock(&pids_lock);
>  }
> 

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