On 2018/08/24 0:49, David Howells wrote:
> I'm seeing the attached message generated from this line:
>
> btrfs_debug_in_rcu(fs_info,
> "btrfs_map_bio: rw %d 0x%x, sector=%llu, dev=%lu (%s id %llu), size=%u",
> bio_op(bio), bio->bi_opf, (u64)bio->bi_iter.bi_sector,
> (u_long)dev->bdev->bd_dev, rcu_str_deref(dev->name), dev->devid,
> bio->bi_iter.bi_size);
>
> in submit_stripe_bio(). I'm not sure exactly why, but I suspect
> rcu_str_deref() is the point from where it is generated.
>
> Note that the mount succeeds.
>
> This code was introduced by:
>
> commit 672d599041c862dd61a1576c32e946ef0d77aa34
> Author: Misono Tomohiro <misono.tomohiro@xxxxxxxxxxxxxx>
> Date: Thu Aug 2 16:19:07 2018 +0900
>
Thanks for the reporting.
I didn't turn on CONFIG_PROVE_RCU and missed the warning.
I will send a fix.
Thanks,
Misono
> David
> ---
> =============================
> WARNING: suspicious RCU usage
> 4.18.0-fscache+ #540 Not tainted
> -----------------------------
> fs/btrfs/volumes.c:6114 suspicious rcu_dereference_check() usage!
>
> other info that might help us debug this:
>
>
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by mount/3194:
> #0: 0000000072604777 (&fc->fs_type->s_umount_key#54/1){+.+.}, at: alloc_super+0xa4/0x313
>
> stack backtrace:
> CPU: 2 PID: 3194 Comm: mount Not tainted 4.18.0-fscache+ #540
> Hardware name: ASUS All Series/H97-PLUS, BIOS 2306 10/09/2014
> Call Trace:
> dump_stack+0x67/0x8e
> btrfs_map_bio+0x282/0x321
> btree_submit_bio_hook+0x71/0xa6
> submit_one_bio+0x55/0x66
> read_extent_buffer_pages+0x1ec/0x2ab
> btree_read_extent_buffer_pages+0x6e/0x237
> ? alloc_extent_buffer+0x28f/0x2f2
> read_tree_block+0x43/0x5e
> open_ctree+0x139b/0x1ee4
> btrfs_get_tree+0x357/0xa33
> ? selinux_fs_context_dup+0x2d/0x104
> vfs_get_tree+0x7a/0x162
> btrfs_mount_root+0x52/0x8b
> btrfs_get_tree+0x4ab/0xa33
> ? vfs_parse_fs_string+0x5b/0x9e
> vfs_get_tree+0x7a/0x162
> do_mount+0x7f0/0x8b2
> ? memdup_user+0x3e/0x5a
> ksys_mount+0x72/0x97
> __x64_sys_mount+0x21/0x24
> do_syscall_64+0x7d/0x1a0
> entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x7f11b8365ada
> Code: 48 8b 0d c9 a3 2b 00 f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 96 a3 2b 00 f7 d8 64 89 01 48
> RSP: 002b:00007ffe0d9a5b98 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
> RAX: ffffffffffffffda RBX: 00005562bf7702a0 RCX: 00007f11b8365ada
> RDX: 00005562bf77a620 RSI: 00005562bf7704a0 RDI: 00005562bf770480
> RBP: 0000000000000000 R08: 0000000000000000 R09: 00007f11b8620c40
> R10: 00000000c0ed0000 R11: 0000000000000246 R12: 00005562bf770480
> R13: 00005562bf77a620 R14: 0000000000000000 R15: 00007f11b90f9184
>
>
