Re: [PATCH] fs: nfs: Fix a sleep-in-atomic bug in nfs_access_add_cache

[Jia-Ju Bai]

On 06/05/2017 07:48 PM, Trond Myklebust wrote:
> On Mon, 2017-06-05 at 16:05 +0800, Jia-Ju Bai wrote:
> > The driver may sleep under a rcu read lock, and function call path
> > is:
> > nfs_permission (acquire the lock by rcu_read_lock)
> >    nfs_do_access
> >      nfs_access_add_cache
> >        kmalloc(GFP_KERNEL) -->  may sleep
> >
> > To fix it, "GFP_KERNEL" is replaced with "GFP_ATOMIC".
> >
> > Signed-off-by: Jia-Ju Bai<baijiaju1990@xxxxxxx>
> > ---
> >   fs/nfs/dir.c |    2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> > index 32ccd77..7a074db 100644
> > --- a/fs/nfs/dir.c
> > +++ b/fs/nfs/dir.c
> > @@ -2333,7 +2333,7 @@ static void nfs_access_add_rbtree(struct inode
> > *inode, struct nfs_access_entry *
> >   
> >   void nfs_access_add_cache(struct inode *inode, struct
> > nfs_access_entry *set)
> >   {
> > -	struct nfs_access_entry *cache = kmalloc(sizeof(*cache),
> > GFP_KERNEL);
> > +	struct nfs_access_entry *cache = kmalloc(sizeof(*cache),
> > GFP_ATOMIC);
> >   	if (cache == NULL)
> >   		return;
> >   	RB_CLEAR_NODE(&cache->rb_node);
> The RCU locked codepath will not ever hit nfs_access_add_rbtree(). It
> returns with an error code of -ECHILD after the test of "may_block".
>
> Cheers
>    Trond
Yes, I think you are right.

Thanks,
Jia-Ju Bai