Messages in this thread | | | Subject | Re: [PATCH 4/4] fs: btrfs: fix a data race in btrfs_block_rsv_release() | From | Jia-Ju Bai <> | Date | Wed, 13 May 2020 10:18:12 +0800 |
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On 2020/5/13 6:18, David Sterba wrote: > On Sat, May 09, 2020 at 01:34:31PM +0800, Jia-Ju Bai wrote: >> The functions btrfs_block_rsv_release() and >> btrfs_update_delayed_refs_rsv() are concurrently executed at runtime in >> the following call contexts: >> >> Thread 1: >> btrfs_file_write_iter() >> btrfs_buffered_write() >> btrfs_delalloc_release_extents() >> btrfs_inode_rsv_release() >> __btrfs_block_rsv_release() >> >> Thread 2: >> finish_ordered_fn() >> btrfs_finish_ordered_io() >> insert_reserved_file_extent() >> __btrfs_drop_extents() >> btrfs_free_extent() >> btrfs_add_delayed_data_ref() >> btrfs_update_delayed_refs_rsv() >> >> In __btrfs_block_rsv_release(): >> else if (... && !delayed_rsv->full) >> >> In btrfs_update_delayed_refs_rsv(): >> spin_lock(&delayed_rsv->lock); >> delayed_rsv->size += num_bytes; >> delayed_rsv->full = 0; >> spin_unlock(&delayed_rsv->lock); >> >> Thus a data race for delayed_rsv->full can occur. >> This race was found and actually reproduced by our conccurency fuzzer. >> >> To fix this race, the spinlock delayed_rsv->lock is used to >> protect the access to delayed_rsv->full in btrfs_block_rsv_release(). >> >> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> >> --- >> fs/btrfs/block-rsv.c | 7 ++++++- >> 1 file changed, 6 insertions(+), 1 deletion(-) >> >> diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c >> index 27efec8f7c5b..89c53a7137b4 100644 >> --- a/fs/btrfs/block-rsv.c >> +++ b/fs/btrfs/block-rsv.c >> @@ -277,6 +277,11 @@ u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info, >> struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv; >> struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv; >> struct btrfs_block_rsv *target = NULL; >> + unsigned short full = 0; >> + >> + spin_lock(&delayed_rsv->lock); >> + full = delayed_rsv->full; >> + spin_unlock(&delayed_rsv->lock); >> >> /* >> * If we are the delayed_rsv then push to the global rsv, otherwise dump >> @@ -284,7 +289,7 @@ u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info, >> */ >> if (block_rsv == delayed_rsv) >> target = global_rsv; >> - else if (block_rsv != global_rsv && !delayed_rsv->full) >> + else if (block_rsv != global_rsv && !full) > This has been reported as suspicous > https://lore.kernel.org/linux-btrfs/CAAwBoOJDjei5Hnem155N_cJwiEkVwJYvgN-tQrwWbZQGhFU=cA@mail.gmail.com/ > > and there's an answer that this is racy but does not cause any > unexpected behaviour.
Okay, thanks :)
Best wishes, Jia-Ju Bai
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