hello Kent Long long no see, glad to hear you again. >> Then two steps: >> A) update k1 to k2 in btree node memory; >> bch_btree_insert_keys(b, op, insert_keys, replace_key) >> B) Write the bset(contains k2) to cache disk by a 30s delay work >> bch_btree_leaf_dirty(b, journal_ref). >> But before the 30s delay work write the bset to cache device, >> these things happend: >> A) GC works, and reclaim the bucket k2 point to; >> B) Allocator works, and invalidate the bucket k2 point to, >> and increase the gen of the bucket, and place it into free_inc >> fifo; >> C) Until now, the 30s delay work still does not finish work, >> so in the disk, the key still is k1, it is dirty and stale >> (its gen is smaller than the gen of the bucket). and then the >> machine power off suddenly happens; >> D) When the machine power on again, after the btree reconstruction, >> the stale dirty key appear. > Only prior to journal replay, right? Or did you uncover something more severe? No, it's after the journal replay, and in write_dirty_finish(), when replace a dirty key with a clean key by calling bch_btree_insert(), no journal will write. >> In bch_extent_bad(), when expensive_debug_checks is off, it would >> treat the dirty key as good even it is stale keys, and it would >> cause bellow probelms: >> A) In read_dirty() it would cause machine crash: >> BUG_ON(ptr_stale(dc->disk.c, &w->key, 0)); >> B) It could be worse when reads hits stale dirty keys, it would >> read old incorrect data. >Neither of these can happen until after journal replay is finished. Prior to >journal replay we expect to find stale dirty keys - if we find any after journal >replay then it's indicative of a real bug. As I said previous, since no journal writes after inserting a replace key in writeback, so this issue has nothing to do with journal. This is a real problem in my environment, after running IO sometimes, I turn off the power suddenly, then turn on the power, and the machine crash in read_dirty() due to the stale && dirty keys.
