diff options
author | Poornima G <pgurusid@redhat.com> | 2016-07-19 15:20:09 +0530 |
---|---|---|
committer | Rajesh Joseph <rjoseph@redhat.com> | 2016-08-11 01:35:17 -0700 |
commit | 26a0b60a01cebda3e88406dd8e13b1b9ed136108 (patch) | |
tree | 9d0a94fdaeb53c54bfb19a6f199f3fbfc420e655 /libglusterfs | |
parent | 757138048fa5d6951dae9114b603f4aae0c8df21 (diff) |
gfapi: Fix IO error caused when there is consecutive graph switches
Backport of http://review.gluster.org/#/c/14722/
This is part 2 of the fix, the part 1 can be found at:
http://review.gluster.org/#/c/14656/
Problem:
=======
Consider a race between, __glfs_active_subvol() and graph_setup().
Lets say @TIME T1:
fs->active_subvol = A
fs->next_subvol = B
__glfs_active_subvol() //under lock fs->mutex
{
....
new_subvol = fs->next_subvol //which is B
.... //Start migration from A to B
__glfs_first_lookup(){
....
unlock fs->mutex //@TIME T2
network fop
lock fs->mutex
....
}
.... //migration continue on B
fs->active_subvol = fs->next_subvol //which is C (explained below)
....
}
@Time T2, lets say in another thread, graph_setup() is called with C,
note that at T2, fs->mutex is unlocked.
graph_stup(C...)
{
lock fs->mutex
....
if (fs->next_subvol) // which is B
destroy subvol (fs->next_subvol)
....
fs->next_subvol = C
....
unlock fs->mutex
}
Thus at the end of this,
fs->old_subvol = A;
fs->active_subvol = C;
fs->next_subvol = NULL;
which is wrong, as B completed migration, but was destroyed by
graph_setup, and C never was migrated.
Solution:
=========
Any new graph can be in one of the 2 states:
- Picked for migration, migration in progress (fs->mip_subvol)
- Not picked so far for migration (fs->next_subvol)
graph_setup() updates fs->next_subvol only, __glfs_active_subvol()
moves fs->next_subvol to fs->mip_subvol and fs->next_subvol = NULL
atomically, and then once the migration is complete, make that the
fs->active_subvol
Change-Id: Ib6ff0565105c5eedb912a43da4017cd413243612
BUG: 1365821
Signed-off-by: Poornima G <pgurusid@redhat.com>
Reviewed-on: http://review.gluster.org/15134
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>
Diffstat (limited to 'libglusterfs')
0 files changed, 0 insertions, 0 deletions