Btrfs: Direct I/O: Fix space accounting
The following call trace is seen when generic/095 test is executed, WARNING: CPU: 3 PID: 2769 at /home/chandan/code/repos/linux/fs/btrfs/inode.c:8967 btrfs_destroy_inode+0x284/0x2a0() Modules linked in: CPU: 3 PID: 2769 Comm: umount Not tainted 4.2.0-rc5+ #31 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20150306_163512-brownie 04/01/2014 ffffffff81c08150 ffff8802ec9cbce8 ffffffff81984058 ffff8802ffd8feb0 0000000000000000 ffff8802ec9cbd28 ffffffff81050385 ffff8802ec9cbd38 ffff8802d12f8588 ffff8802d12f8588 ffff8802f15ab000 ffff8800bb96c0b0 Call Trace: [<ffffffff81984058>] dump_stack+0x45/0x57 [<ffffffff81050385>] warn_slowpath_common+0x85/0xc0 [<ffffffff81050465>] warn_slowpath_null+0x15/0x20 [<ffffffff81340294>] btrfs_destroy_inode+0x284/0x2a0 [<ffffffff8117ce07>] destroy_inode+0x37/0x60 [<ffffffff8117cf39>] evict+0x109/0x170 [<ffffffff8117cfd5>] dispose_list+0x35/0x50 [<ffffffff8117dd3a>] evict_inodes+0xaa/0x100 [<ffffffff81165667>] generic_shutdown_super+0x47/0xf0 [<ffffffff81165951>] kill_anon_super+0x11/0x20 [<ffffffff81302093>] btrfs_kill_super+0x13/0x110 [<ffffffff81165c99>] deactivate_locked_super+0x39/0x70 [<ffffffff811660cf>] deactivate_super+0x5f/0x70 [<ffffffff81180e1e>] cleanup_mnt+0x3e/0x90 [<ffffffff81180ebd>] __cleanup_mnt+0xd/0x10 [<ffffffff81069c06>] task_work_run+0x96/0xb0 [<ffffffff81003a3d>] do_notify_resume+0x3d/0x50 [<ffffffff8198cbc2>] int_signal+0x12/0x17 This means that the inode had non-zero "outstanding extents" during eviction. This occurs because, during direct I/O a task which successfully used up its reserved data space would set BTRFS_INODE_DIO_READY bit and does not clear the bit after finishing the DIO write. A future DIO write could actually fail and the unused reserve space won't be freed because of the previously set BTRFS_INODE_DIO_READY bit. Clearing the BTRFS_INODE_DIO_READY bit in btrfs_direct_IO() caused the following issue, |-----------------------------------+-------------------------------------| | Task A | Task B | |-----------------------------------+-------------------------------------| | Start direct i/o write on inode X.| | | reserve space | | | Allocate ordered extent | | | release reserved space | | | Set BTRFS_INODE_DIO_READY bit. | | | | splice() | | | Transfer data from pipe buffer to | | | destination file. | | | - kmap(pipe buffer page) | | | - Start direct i/o write on | | | inode X. | | | - reserve space | | | - dio_refill_pages() | | | - sdio->blocks_available == 0 | | | - Since a kernel address is | | | being passed instead of a | | | user space address, | | | iov_iter_get_pages() returns | | | -EFAULT. | | | - Since BTRFS_INODE_DIO_READY is | | | set, we don't release reserved | | | space. | | | - Clear BTRFS_INODE_DIO_READY bit.| | -EIOCBQUEUED is returned. | | |-----------------------------------+-------------------------------------| Hence this commit introduces "struct btrfs_dio_data" to track the usage of reserved data space. The remaining unused "reserve space" can now be freed reliably. Signed-off-by:Chandan Rajendra <chandan@linux.vnet.ibm.com> Reviewed-by:
Liu Bo <bo.li.liu@oracle.com> Signed-off-by:
Chris Mason <clm@fb.com>
parent
a30e577c
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