Merge #20972: locks: Annotate CTxMemPool::check to require cs_main

b396467 locks: Annotate CTxMemPool::check to require cs_main (Carl Dong)

Pull request description:

  ```
  Currently, CTxMemPool::check locks CTxMemPool's own cs member, then
  calls GetSpendHeight which locks cs_main. This can potentially cause an
  undesirable lock invesion since CTxMemPool's cs is supposed to be locked
  after cs_main.

  This does not cause us any problems right now because all callers of
  CTxMemPool already lock cs_main before calling CTxMemPool::check, which
  means that the LOCK(cs_main) in GetSpendHeight becomes benign.

  However, it is currently possible for new code to be added which calls
  CTxMemPool::check without locking cs_main (which would be dangerous).
  Therefore we should make it explicit that cs_main needs to be held
  before calling CTxMemPool::check.

  NOTE: After all review-only assertions are removed in "#20158 |
        tree-wide: De-globalize ChainstateManager", and assuming that we
        keep the changes in "validation: Pass in spendheight to
        CTxMemPool::check", we can re-evaluate to see if this annotation
        is still necessary.
  ```
  -----

  Previous discussions:
  1. bitcoin/bitcoin#20158 (comment)
  2. bitcoin/bitcoin#20158 (review)
  3. bitcoin/bitcoin#20749 (comment)

ACKs for top commit:
  jnewbery:
    Code review ACK b396467
  MarcoFalke:
    ACK b396467
  jonatack:
    ACK b396467 review and debug built, verified that `cs_main` is held by callers of `CTxMemPool::check()` in `PeerManagerImpl::ProcessOrphanTx()`, `PeerManagerImpl::ProcessMessage()`, and `CChainState::ActivateBestChainStep()`

Tree-SHA512: 4635cddb4aa1af9532bb657b2f9c4deec4568d16ba28c574eae91bb77368cd40e23c3c720a9de11cec78e7ad678a44a5e25af67f13214b86b56e777e0c35a026

Author: MarcoFalke

src/txmempool.cpp

@@ -618,6 +618,7 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
 
     if (GetRand(m_check_ratio) >= 1) return;
 
+    AssertLockHeld(::cs_main);
     LOCK(cs);
     LogPrint(BCLog::MEMPOOL, "Checking mempool with %u transactions and %u inputs\n", (unsigned int)mapTx.size(), (unsigned int)mapNextTx.size());
 

src/txmempool.h

@@ -602,7 +602,7 @@ class CTxMemPool
      * all inputs are in the mapNextTx array). If sanity-checking is turned off,
      * check does nothing.
      */
-    void check(const CCoinsViewCache *pcoins) const;
+    void check(const CCoinsViewCache *pcoins) const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     // addUnchecked must updated state for all ancestors of a given transaction,
     // to track size/count of descendant transactions.  First version of