On Wed, Feb 17, 2021 at 10:09 PM Qu Wenruo <quwenruo.bt...@gmx.com> wrote:
> On 2021/2/18 下午1:49, Erik Jensen wrote:
> > On Wed, Feb 17, 2021 at 9:24 PM Qu Wenruo <quwenruo.bt...@gmx.com> wrote:
> >> Got it now.
> >>
> >> [ 295.249182] read_extent_buffer_pages: eb->start=26207780683776 mirror=0
> >> [ 295.249188] __btrfs_map_block: logical=8615594639360 chunk
> >> start=8614760677376 len=4294967296 type=0x81
> >> [ 295.249189] __btrfs_map_block: stripe[0] devid=3 phy=2118735708160
> >>
> >> Note that, the initial request is to read from 26207780683776.
> >> But inside btrfs_map_block(), we want to read from 8615594639360.
> >>
> >> This is totally screwed up in a unexpected way.
> >>
> >> 26207780683776 = 0x17d5f9754000
> >> 8615594639360 = 0x07d5f9754000
> >>
> >> See the missing leading 1, which screws up the result.
> >>
> >> The problem should be the logical calculation part, which doesn't do
> >> proper u64 conversion which could cause the problem.
> >>
> >> Would you like to test the single line fix below?
> >>
> >> Thanks,
> >> Qu
> >>
> >> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> >> index b8fab44394f5..69d728f5ff9e 100644
> >> --- a/fs/btrfs/volumes.c
> >> +++ b/fs/btrfs/volumes.c
> >> @@ -6575,7 +6575,7 @@ blk_status_t btrfs_map_bio(struct btrfs_fs_info
> >> *fs_info, struct bio *bio,
> >> {
> >> struct btrfs_device *dev;
> >> struct bio *first_bio = bio;
> >> - u64 logical = bio->bi_iter.bi_sector << 9;
> >> + u64 logical = ((u64)bio->bi_iter.bi_sector) << 9;
> >> u64 length = 0;
> >> u64 map_length;
> >> int ret;
> >
> > So… it appears my kernel tree (Arch32's 5.10.14-arch1) already has that:
> >
>
> And I also noticed that since v5.2 kernel, we should already have
> bi_sector as u64.
>
> So why that left shift would get higher bits missing is really strange.
> Especially the missing part is just at the 45 bit, not 32 bit boundary.
>
> Then what about this diff? It goes multiplying other than using
> dangerous left shift.
>
> (Also, it's recommended to still use previous debug diffs, so if it
> doesn't work we still have a chance to know what's going wrong).
>
> Thanks,
> Qu
No change. I added an extra debug line in btrfs_map_bio, and get the following:
btrfs_map_bio: bio->bi_iter.bi_sector=16827333280, logical=8615594639360
bio->bi_iter.bi_sector is 16827333280, not 51187071648, so it looks
like the top bit is already missing before the shift / multiplication.
