Revert "fix too early close of shared lock file"

This reverts commit 66b2536ea0.

I misunderstood commit ac56a5c2a0
and caused a FD leak when pid locking is not used.

A LockHandle contains an action that will close the underlying lock
file, and that action is run when it is closed. In the case of a shared
lock, the lock file is opened once for each LockHandle, and only
the one for the LockHandle that is being closed will be closed.

CHANGELOG

@@ -6,7 +6,6 @@ git-annex (8.20211124) UNRELEASED; urgency=medium
     erroring out.
   * export: Avoid unncessarily re-exporting non-annexed files that were
     already exported.
-  * Fix locking bug introduced in version 8.20200814.
   * Fix locking problems when annex.pidlock is set and concurrency is
     enabled eg with -J.
 

Utility/LockPool/STM.hs

@@ -28,7 +28,6 @@ import System.FilePath.ByteString (RawFilePath)
 import qualified Data.Map.Strict as M
 import Control.Concurrent.STM
 import Control.Exception
-import Control.Monad
 
 type LockFile = RawFilePath
 
@@ -129,8 +128,8 @@ getLockStatus pool file getdefault checker = do
 		Nothing -> getdefault
 		Just restore -> bracket_ (return ()) restore checker
 
--- Only runs action to close underlying lock file when this is the last
--- user of the lock, and when the lock has not already been closed.
+-- Releases the lock. When it is a shared lock, it may remain locked by
+-- other LockHandles.
 --
 -- Note that the lock pool is left empty while the CloseLockFile action
 -- is run, to avoid race with another thread trying to open the same lock
@@ -139,15 +138,15 @@ releaseLock :: LockHandle -> IO ()
 releaseLock h = go =<< atomically (tryTakeTMVar h)
   where
 	go (Just (pool, file, closelockfile)) = do
-		(m, lastuser) <- atomically $ do
+		m <- atomically $ do
 			m <- takeTMVar pool
 			return $ case M.lookup file m of
 				Just (LockStatus mode n firstlocksem)
-					| n == 1 -> (M.delete file m, True)
+					| n == 1 -> (M.delete file m)
 					| otherwise ->
-						(M.insert file (LockStatus mode (pred n) firstlocksem) m, False)
-				Nothing -> (m, True)
-		() <- when lastuser closelockfile
+						(M.insert file (LockStatus mode (pred n) firstlocksem) m)
+				Nothing -> m
+		() <- closelockfile
 		atomically $ putTMVar pool m
 	-- The LockHandle was already closed.
 	go Nothing = return ()

doc/bugs/annex_get_should_retry_failed_downloads_from_S3/comment_9_df98c47016e79f15218880a009e671ea._comment

@@ -0,0 +1,14 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 9"""
+ date="2021-12-06T16:36:45Z"
+ content="""
+Unfortunately, [[!commit 66b2536ea0aa5c88f5b744eeace3322a8a4a10b6]]
+broke shared locking when pid locks are not used, causing a FD leak,
+and had to be reverted. Which further breaks concurrent pid locking. 
+
+At this point, when -J is used with pidlock, it may drop the lock but
+still think it has it held internally. Comment #7 found another way that
+could happen, and the conclusion is that the pid lock must migrate away
+from using the lock pool.
+"""]]