• Tejun Heo's avatar
    writeback: don't drain bdi_writeback_congested on bdi destruction · a20135ff
    Tejun Heo authored
    52ebea74 ("writeback: make backing_dev_info host cgroup-specific
    bdi_writebacks") made bdi (backing_dev_info) host per-cgroup wb's
    (bdi_writeback's).  As the congested state needs to be per-wb and
    referenced from blkcg side and multiple wbs, the patch made all
    non-root cong's (bdi_writeback_congested's) reference counted and
    indexed on bdi.
    When a bdi is destroyed, cgwb_bdi_destroy() tries to drain all
    non-root cong's; however, this can hang indefinitely because wb's can
    also be referenced from blkcg_gq's which are destroyed after bdi
    destruction is complete.
    This patch fixes the bug by updating bdi destruction to not wait for
    cong's to drain.  A cong is unlinked from bdi->cgwb_congested_tree on
    bdi destuction regardless of its reference count as the bdi may go
    away any point after destruction.  wb_congested_put() checks whether
    the cong is already unlinked on release.
    Signed-off-by: default avatarTejun Heo <tj@kernel.org>
    Reported-by: default avatarJon Christopherson <jon@jons.org>
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=100681
    Fixes: 52ebea74 ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks")
    Tested-by: default avatarJon Christopherson <jon@jons.org>
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
backing-dev.c 25.5 KB