Re: fs/btrfs/volumes.c:6114 suspicious rcu_dereference_check() usage!

[David Howells <dhowells@redhat.com>]

David Sterba <dsterba@suse.cz> wrote:

> The code previously had explicit rcu_lock/unlock, now it uses the
> btrfs_debug_in_rcu helper which is supposed to provide that. It's
> possible that the helper is missing it due to some #ifdef mess, but I
> don't see it.

I preprocessed the function and extracted submit_stripe_bio() (see attached).

The problem is that btrfs_no_printk() is being called, but not within an RCU
section.

#define btrfs_debug_in_rcu(fs_info, fmt, args...) \
	btrfs_printk_in_rcu(fs_info, KERN_DEBUG fmt, ##args)

David
---
static void submit_stripe_bio(struct btrfs_bio *bbio, struct bio *bio,
         u64 physical, int dev_nr, int async)
{
 struct btrfs_device *dev = bbio->stripes[dev_nr].dev;
 struct btrfs_fs_info *fs_info = bbio->fs_info;

 bio->bi_private = bbio;
 btrfs_io_bio(bio)->stripe_index = dev_nr;
 bio->bi_end_io = btrfs_end_bio;
 bio->bi_iter.bi_sector = physical >> 9;
 btrfs_no_printk(fs_info, "\001" "7" "btrfs_map_bio: rw %d 0x%x, sector=%llu, dev=%lu (%s id %llu), size=%u", ((bio)->bi_opf & ((1 << 8) - 1)), bio->bi_opf, (u64)bio->bi_iter.bi_sector, (u_long)dev->bdev->bd_dev, ({ struct rcu_string *__str = ({ typeof(*(dev->name)) *________p1 = (typeof(*(dev->name)) *)({ union { typeof((dev->name)) __val; char __c[1]; } __u; if (1) __read_once_size(&((dev->name)), __u.__c, sizeof((dev->name))); else __read_once_size_nocheck(&((dev->name)), __u.__c, sizeof((dev->name))); do { } while (0); __u.__val; }); do { static bool __attribute__ ((__section__(".data.unlikely"))) __warned; if (debug_lockdep_rcu_enabled() && !__warned && (!((0) || rcu_read_lock_held()))) { __warned = true; lockdep_rcu_suspicious(



                      "fs/btrfs/volumes.c"
# 6110 "../fs/btrfs/volumes.c"
 ,



                      6114
# 6110 "../fs/btrfs/volumes.c"
 , "suspicious rcu_dereference_check() usage"); } } while (0); ; ((typeof(*(dev->name)) *)(________p1)); }); __str->str; }), dev->devid, bio->bi_iter.bi_size)



                       ;
 do { if ((bio)->bi_disk != (dev->bdev)->bd_disk) bio_clear_flag(bio, 9); (bio)->bi_disk = (dev->bdev)->bd_disk; (bio)->bi_partno = (dev->bdev)->bd_partno; } while (0);

 btrfs_bio_counter_inc_noblocked(fs_info);

 if (async)
  btrfs_schedule_bio(dev, bio);
 else
  btrfsic_submit_bio(bio);
}