Disk failure->Error message indicates bug

Quoted 3 lines · Neil Brown

- md2 checks b_rdev to see which device was in error. It gets confused because sda12 is not part of md2.

Quoted 3 lines

The fix probably involves making sure that b_dev really does refer to md0 (a quick look at the code suggests it actually refers to md2!) and then using b_dev instead of b_rdev.

the fix i think is to not look at b_rdev in the error path (and anywhere else), at all. Just like we dont look at rsector.

Do we need that
information? b_rdev is in fact just for RAID0 and LINEAR, and i believe it would be cleaner to get rid of it altogether, and create a new encapsulated bh for every RAID0 request, like we do it in RAID1/RAID5. OTOH handling this is clearly more complex than RAID0 itself.

Quoted 2 lines

Basically, b_rdev and b_rsector cannot be trusted after a call to make_request, but they are being trusted.

yep. What about this solution:

md.c (or buffer.c) implements a generic pool of IO-related buffer-heads. This pool would have deadlock assurance, and allocation from this pool could never fail. This would already reduce the complexity of raid1.c and raid5.c bh-allocation. Then raid0.c and linear.c is changed to create a new bh for the mapping, which is hung off bh->b_dev_id. bh->b_rdev would be gone, ll_rw_blk looks at bh->b_dev. This also simplifies the handling of bhs.

i like this solution much better, and i dont think there is any significant performance impact (starting IO is heavy anyway), but it would clean up this issue for once and for all.