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authorPoornima G <pgurusid@redhat.com>2016-07-19 15:20:09 +0530
committerKaushal M <kaushal@redhat.com>2016-08-24 21:42:50 -0700
commit9df752213e6f8a1cc9a5e875cf68ca8ef32f61db (patch)
tree1872f4e487433ff55ef001b7f680634001f461ec /xlators
parent9cd5066226770cf3c06a21757b963d315b8fe32b (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 > Reviewed-on: http://review.gluster.org/14722 > 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: Raghavendra Talur <rtalur@redhat.com> > Reviewed-by: Rajesh Joseph <rjoseph@redhat.com> > Reviewed-by: Niels de Vos <ndevos@redhat.com> BUG: 1367294 Change-Id: Ib6ff0565105c5eedb912a43da4017cd413243612 Signed-off-by: Poornima G <pgurusid@redhat.com> Signed-off-by: Oleksandr Natalenko <oleksandr@natalenko.name> Reviewed-on: http://review.gluster.org/15167 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: Kaushal M <kaushal@redhat.com>
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