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fix drop hang reported by musicmatze

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Fix hang when dropping content needs to lock the content on a ssh remote,
which occurred when the remote has git-annex version 5.20151019 or newer.

Analysis: `race` runs 2 threads at once, and the hGetLine finishes first.
So, it tries to cancel the waitForProcess, but unfortunately that is making
a foreign call and so cannot be canceled. The remote git-annex-shell
is waiting for a line on stdin before it will exit. Deadlock.

This only occurred sometimes; I reproduced it going from darkstar to
elephant, but not from darkstar to darkstar. Not sure how that fits into
the above analysis -- perhaps a race condition is also involved?

Fixed by not using `race`; now the hGetLine will fail with an exception
if the remote git-annex-shell exits without any output.
This commit is contained in:
Joey Hess 2016-04-18 14:04:20 -04:00
parent f24dba7616
commit 2d7e46ea98
Failed to extract signature
2 changed files with 13 additions and 12 deletions
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21
Remote/Git.hs
View file

@ -57,7 +57,6 @@ import Types.NumCopies
import Control.Concurrent import Control.Concurrent
import Control.Concurrent.MSampleVar import Control.Concurrent.MSampleVar
import Control.Concurrent.Async
import qualified Data.Map as M import qualified Data.Map as M
import Network.URI import Network.URI
@ -387,17 +386,14 @@ lockKey r key callback
, std_out = CreatePipe , std_out = CreatePipe
, std_err = UseHandle nullh , std_err = UseHandle nullh
} }
-- Wait for either the process to exit, or for it to v <- liftIO $ tryIO $ hGetLine hout
-- indicate the content is locked. let signaldone = void $ tryNonAsync $ liftIO $ mapM_ tryNonAsync
v <- liftIO $ race [ hPutStrLn hout ""
(waitForProcess p) , hFlush hout
(hGetLine hout) , hClose hin
let signaldone = void $ tryNonAsync $ liftIO $ do , hClose hout
hPutStrLn hout "" , void $ waitForProcess p
hFlush hout ]
hClose hin
hClose hout
void $ waitForProcess p
let checkexited = not . isJust <$> getProcessExitCode p let checkexited = not . isJust <$> getProcessExitCode p
case v of case v of
Left _exited -> do Left _exited -> do
@ -405,6 +401,7 @@ lockKey r key callback
liftIO $ do liftIO $ do
hClose hin hClose hin
hClose hout hClose hout
void $ waitForProcess p
failedlock failedlock
Right l Right l
| l == Ssh.contentLockedMarker -> bracket_ | l == Ssh.contentLockedMarker -> bracket_

4
debian/changelog vendored
View file

@ -17,6 +17,10 @@ git-annex (6.20160413) UNRELEASED; urgency=medium
* fsck: Warn when core.sharedRepository is set and an annex object file's * fsck: Warn when core.sharedRepository is set and an annex object file's
write bit is not set and cannot be set due to the file being owned write bit is not set and cannot be set due to the file being owned
by a different user. by a different user.
* Fix hang when dropping content needs to lock the content on a
ssh remote, which occurred when the remote has git-annex version
5.20151019 or newer. (The bug was in the client side; the remote
git-annex-shell does not need to be upgraded.)
-- Joey Hess <id@joeyh.name> Wed, 13 Apr 2016 13:30:32 -0400 -- Joey Hess <id@joeyh.name> Wed, 13 Apr 2016 13:30:32 -0400