Message ID | 20200509053431.3860-1-baijiaju1990@gmail.com (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | None | expand |
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.
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
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) target = delayed_rsv; if (target && block_rsv->space_info != target->space_info)
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(-)