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04e484c597
[BUG]
The following small test script can trigger ASSERT() at unmount time:
mkfs.btrfs -f $dev
mount $dev $mnt
mount -o remount,discard=async $mnt
umount $mnt
The call trace:
assertion failed: atomic_read(&block_group->count) == 1, in fs/btrfs/block-group.c:3431
------------[ cut here ]------------
kernel BUG at fs/btrfs/ctree.h:3204!
invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
CPU: 4 PID: 10389 Comm: umount Tainted: G O 5.8.0-rc3-custom+ #68
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
Call Trace:
btrfs_free_block_groups.cold+0x22/0x55 [btrfs]
close_ctree+0x2cb/0x323 [btrfs]
btrfs_put_super+0x15/0x17 [btrfs]
generic_shutdown_super+0x72/0x110
kill_anon_super+0x18/0x30
btrfs_kill_super+0x17/0x30 [btrfs]
deactivate_locked_super+0x3b/0xa0
deactivate_super+0x40/0x50
cleanup_mnt+0x135/0x190
__cleanup_mnt+0x12/0x20
task_work_run+0x64/0xb0
__prepare_exit_to_usermode+0x1bc/0x1c0
__syscall_return_slowpath+0x47/0x230
do_syscall_64+0x64/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xa9
The code:
ASSERT(atomic_read(&block_group->count) == 1);
btrfs_put_block_group(block_group);
[CAUSE]
Obviously it's some btrfs_get_block_group() call doesn't get its put
call.
The offending btrfs_get_block_group() happens here:
void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
{
if (list_empty(&bg->bg_list)) {
btrfs_get_block_group(bg);
list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
}
}
So every call sites removing the block group from unused_bgs list should
reduce the ref count of that block group.
However for async discard, it didn't follow the call convention:
void btrfs_discard_punt_unused_bgs_list(struct btrfs_fs_info *fs_info)
{
list_for_each_entry_safe(block_group, next, &fs_info->unused_bgs,
bg_list) {
list_del_init(&block_group->bg_list);
btrfs_discard_queue_work(&fs_info->discard_ctl, block_group);
}
}
And in btrfs_discard_queue_work(), it doesn't call
btrfs_put_block_group() either.
[FIX]
Fix the problem by reducing the reference count when we grab the block
group from unused_bgs list.
Reported-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Fixes:
|
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.