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SubjectRe: [PATCH v2] writeback: inode cgroup wb switch should not call ihold()
On Wed 15-06-16 13:35:10, Tahsin Erdogan wrote:
> Asynchronous wb switching of inodes takes an additional ref count on an
> inode to make sure inode remains valid until switchover is completed.
>
> However, anyone calling ihold() must already have a ref count on inode,
> but in this case inode->i_count may already be zero:
>
> ------------[ cut here ]------------
> WARNING: CPU: 1 PID: 917 at fs/inode.c:397 ihold+0x2b/0x30
> CPU: 1 PID: 917 Comm: kworker/u4:5 Not tainted 4.7.0-rc2+ #49
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs
> 01/01/2011
> Workqueue: writeback wb_workfn (flush-8:16)
> 0000000000000000 ffff88007ca0fb58 ffffffff805990af 0000000000000000
> 0000000000000000 ffff88007ca0fb98 ffffffff80268702 0000018d000004e2
> ffff88007cef40e8 ffff88007c9b89a8 ffff880079e3a740 0000000000000003
> Call Trace:
> [<ffffffff805990af>] dump_stack+0x4d/0x6e
> [<ffffffff80268702>] __warn+0xc2/0xe0
> [<ffffffff802687d8>] warn_slowpath_null+0x18/0x20
> [<ffffffff8035b4ab>] ihold+0x2b/0x30
> [<ffffffff80367ecc>] inode_switch_wbs+0x11c/0x180
> [<ffffffff80369110>] wbc_detach_inode+0x170/0x1a0
> [<ffffffff80369abc>] writeback_sb_inodes+0x21c/0x530
> [<ffffffff80369f7e>] wb_writeback+0xee/0x1e0
> [<ffffffff8036a147>] wb_workfn+0xd7/0x280
> [<ffffffff80287531>] ? try_to_wake_up+0x1b1/0x2b0
> [<ffffffff8027bb09>] process_one_work+0x129/0x300
> [<ffffffff8027be06>] worker_thread+0x126/0x480
> [<ffffffff8098cde7>] ? __schedule+0x1c7/0x561
> [<ffffffff8027bce0>] ? process_one_work+0x300/0x300
> [<ffffffff80280ff4>] kthread+0xc4/0xe0
> [<ffffffff80335578>] ? kfree+0xc8/0x100
> [<ffffffff809903cf>] ret_from_fork+0x1f/0x40
> [<ffffffff80280f30>] ? __kthread_parkme+0x70/0x70
> ---[ end trace aaefd2fd9f306bc4 ]---
>
> Acked-by: Tejun Heo <tj@kernel.org>
> Signed-off-by: Tahsin Erdogan <tahsin@google.com>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

--
Jan Kara <jack@suse.com>
SUSE Labs, CR

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