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f2fs: fix potential panic during fstrim

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As Ju Hyung Park reported:

"When 'fstrim' is called for manual trim, a BUG() can be triggered
randomly with this patch.

I'm seeing this issue on both x86 Desktop and arm64 Android phone.

On x86 Desktop, this was caused during Ubuntu boot-up. I have a
cronjob installed which calls 'fstrim -v /' during boot. On arm64
Android, this was caused during GC looping with 1ms gc_min_sleep_time
& gc_max_sleep_time."

Root cause of this issue is that f2fs_wait_discard_bios can only be
used by f2fs_put_super, because during put_super there must be no
other referrers, so it can ignore discard entry's reference count
when removing the entry, otherwise in other caller we will hit bug_on
in __remove_discard_cmd as there may be other issuer added reference
count in discard entry.

Thread A				Thread B
					- issue_discard_thread
- f2fs_ioc_fitrim
 - f2fs_trim_fs
  - f2fs_wait_discard_bios
   - __issue_discard_cmd
    - __submit_discard_cmd
					 - __wait_discard_cmd
					  - dc->ref++
					  - __wait_one_discard_bio
   - __wait_discard_cmd
    - __remove_discard_cmd
     - f2fs_bug_on(sbi, dc->ref)

Fixes: 969d1b180d
Reported-by: Ju Hyung Park <qkrwngud825@gmail.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Chao Yu
2017-10-02 02:50:16 +08:00
committed by Jaegeuk Kim
parent e365806ac2
commit 638164a271
3 changed files with 5 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
fs/f2fs/segment.c
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@@ -1210,11 +1210,11 @@ void stop_discard_thread(struct f2fs_sb_info *sbi)
}
/* This comes from f2fs_put_super and f2fs_trim_fs */
void f2fs_wait_discard_bios(struct f2fs_sb_info *sbi)
void f2fs_wait_discard_bios(struct f2fs_sb_info *sbi, bool umount)
{
__issue_discard_cmd(sbi, false);
__drop_discard_cmd(sbi);
__wait_discard_cmd(sbi, false);
__wait_discard_cmd(sbi, !umount);
}
static void mark_discard_range_all(struct f2fs_sb_info *sbi)
@@ -2244,7 +2244,7 @@ int f2fs_trim_fs(struct f2fs_sb_info *sbi, struct fstrim_range *range)
}
/* It's time to issue all the filed discards */
mark_discard_range_all(sbi);
f2fs_wait_discard_bios(sbi);
f2fs_wait_discard_bios(sbi, false);
out:
range->len = F2FS_BLK_TO_BYTES(cpc.trimmed);
return err;