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| author | Marko Mäkelä <marko.makela@mariadb.com> | 2021-04-22 15:43:30 +0300 |
|---|---|---|
| committer | Marko Mäkelä <marko.makela@mariadb.com> | 2021-04-22 15:43:30 +0300 |
| commit | 8121d03fd48c5107a2ef04b3d9991e1441e92995 (patch) | |
| tree | 07a7cab57bae88bb5054483e8363f86b3847ff72 | |
| parent | 54c460ace606157f2a23706ec98e9de70aba767e (diff) | |
| download | mariadb-git-bb-10.6-MDEV-25404.tar.gz | |
MDEV-25404 fixup: Fix ssux_lock_low::u_wr_upgrade()bb-10.6-MDEV-25404
The U-to-X upgrade turned out to be incorrect. A debug assertion
failed in wr_wait(), called from mtr_defer_drop_ahi() in a stress
test with innodb_adaptive_hash_index=ON.
A correct upgrade procedure ought to be readers.fetch_add(WRITER-1)
to register ourselves as a WRITER (or waiting writer) and to release
the reference that was being held for the U lock.
Thanks to Matthias Leich for catching the problem.
| -rw-r--r-- | storage/innobase/include/srw_lock.h | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/storage/innobase/include/srw_lock.h b/storage/innobase/include/srw_lock.h index a74cb9a9212..fdac659d494 100644 --- a/storage/innobase/include/srw_lock.h +++ b/storage/innobase/include/srw_lock.h @@ -217,11 +217,9 @@ public: void u_wr_upgrade() { DBUG_ASSERT(writer.is_locked()); - uint32_t lk= 1; - if (!readers.compare_exchange_strong(lk, WRITER, - std::memory_order_acquire, - std::memory_order_relaxed)) - wr_wait(lk); + uint32_t lk= readers.fetch_add(WRITER - 1, std::memory_order_acquire); + if (lk != 1) + wr_wait(lk - 1); } void wr_u_downgrade() { |