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cluster/ec: lk shouldn't be a transaction

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Problem:
When application sends a blocking lock, the lk fop actually waits under
inodelk.  This can lead to a dead-lock.
1) Let's say app-1 takes exculsive-fcntl-lock on the file
2) app-2 attempts an exclusive-fcntl-lock on the file which goes to blocking
   stage note: app-2 is blocked inside transaction which holds an inode-lock
3) app-1 tries to perform write which needs inode-lock so it gets blocked on
   app-2 to unlock inodelk and app-2 is blocked on app-1 to unlock fcntl-lock

Fix:
Correct way to fix this issue and make fcntl locks perform well would be to
introduce
2-phase locking for fcntl lock:
1) Implement a try-lock phase where locks xlator will not merge lk call with
   existing calls until a commit-lock phase.
2) If in try-lock phase we get quorum number of success without any EAGAIN
   error, then send a commit-lock which will merge locks.
3) In case there are any errors, unlock should just delete the lock-object
   which was tried earlier and shouldn't touch the committed locks.

Unfortunately this is a sizeable feature and need to be thought through for any
corner cases.  Until then remove transaction from lk call.

BUG: 1455049
Change-Id: I18a782903ba0eb43f1e6526fb0cf8c626c460159
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: https://review.gluster.org/17542
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Ashish Pandey <aspandey@redhat.com>
Reviewed-by: Xavier Hernandez <xhernandez@datalab.es>
This commit is contained in:
Pranith Kumar K 2017-06-13 23:35:40 +05:30 committed by Xavier Hernandez
parent f0fb166078
commit 26ca39ccf0
1 changed files with 1 additions and 19 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
xlators/cluster/ec/src/ec-locks.c
View File

@ -1020,12 +1020,6 @@ int32_t ec_manager_lk(ec_fop_data_t * fop, int32_t state)
/* Fall through */
case EC_STATE_LOCK:
ec_lock_prepare_fd(fop, fop->fd, EC_UPDATE_DATA | EC_QUERY_INFO);
ec_lock(fop);
return EC_STATE_DISPATCH;
case EC_STATE_DISPATCH:
ec_dispatch_all(fop);
@ -1080,10 +1074,9 @@ int32_t ec_manager_lk(ec_fop_data_t * fop, int32_t state)
cbk->op_errno, &cbk->flock, cbk->xdata);
}
return EC_STATE_LOCK_REUSE;
return EC_STATE_END;
case -EC_STATE_INIT:
case -EC_STATE_LOCK:
case -EC_STATE_DISPATCH:
case -EC_STATE_REPORT:
GF_ASSERT(fop->error != 0);
@ -1094,17 +1087,6 @@ int32_t ec_manager_lk(ec_fop_data_t * fop, int32_t state)
NULL, NULL);
}
return EC_STATE_LOCK_REUSE;
case -EC_STATE_LOCK_REUSE:
case EC_STATE_LOCK_REUSE:
ec_lock_reuse(fop);
return EC_STATE_UNLOCK;
case -EC_STATE_UNLOCK:
case EC_STATE_UNLOCK:
ec_unlock(fop);
return EC_STATE_END;