Re: [f2fs-dev] [PATCH] f2fs: do not use mutex lock in atomic context

[Ritesh Harjani]

On 2/15/2019 2:40 PM, Chao Yu wrote:
> On 2019/2/15 12:28, Ritesh Harjani wrote:
> > On 2/14/2019 9:40 PM, Chao Yu wrote:
> > > On 2019-2-14 15:46, Sahitya Tummala wrote:
> > > > On Wed, Feb 13, 2019 at 11:25:31AM +0800, Chao Yu wrote:
> > > > > 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@xxxxxxxxxxxxxx>
> > > > > > ---
> > > > > >    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);
> > Do you know why do we have a retry logic here? When anyways we have
> > called for radix_tree_delete with pid key?
> > Which should ensure the slot is empty, no?
> > Then why in the original code (f2fs_radix_tree_insert), we were
> > retrying. For what condition a retry was needed?
> Hi,
>
> f2fs_radix_tree_insert is used in many places, it was introduced to used in
> some paths we should not failed.
>
> And here, I guess we used it for the same purpose, if we failed to insert
> @current pointer into radix, next time, we may not skip calling
> trace_printk, actually it will print the same current->comm info as
> previous one, it's redundant.

Sure, thanks for the info.

Regards
Ritesh