From: "Darrick J. Wong" djwong@kernel.org
commit 03e0add80f4cf3f7393edb574eeb3a89a1db7758 upstream.
I've been noticing odd racing behavior in the inodegc code that could only be explained by one cpu adding an inode to its inactivation llist at the same time that another cpu is processing that cpu's llist. Preemption is disabled between get/put_cpu_ptr, so the only explanation is scheduler mayhem. I inserted the following debug code into xfs_inodegc_worker (see the next patch):
ASSERT(gc->cpu == smp_processor_id());
This assertion tripped during overnight tests on the arm64 machines, but curiously not on x86_64. I think we haven't observed any resource leaks here because the lockfree list code can handle simultaneous llist_add and llist_del_all functions operating on the same list. However, the whole point of having percpu inodegc lists is to take advantage of warm memory caches by inactivating inodes on the last processor to touch the inode.
The incorrect scheduling seems to occur after an inodegc worker is subjected to mod_delayed_work(). This wraps mod_delayed_work_on with WORK_CPU_UNBOUND specified as the cpu number. Unbound allows for scheduling on any cpu, not necessarily the same one that scheduled the work.
Because preemption is disabled for as long as we have the gc pointer, I think it's safe to use current_cpu() (aka smp_processor_id) to queue the delayed work item on the correct cpu.
Fixes: 7cf2b0f9611b ("xfs: bound maximum wait time for inodegc work") Signed-off-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Dave Chinner dchinner@redhat.com Signed-off-by: Dave Chinner david@fromorbit.com Signed-off-by: Amir Goldstein amir73il@gmail.com Acked-by: Darrick J. Wong djwong@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/xfs/xfs_icache.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
--- a/fs/xfs/xfs_icache.c +++ b/fs/xfs/xfs_icache.c @@ -2052,7 +2052,8 @@ xfs_inodegc_queue( queue_delay = 0;
trace_xfs_inodegc_queue(mp, __return_address); - mod_delayed_work(mp->m_inodegc_wq, &gc->work, queue_delay); + mod_delayed_work_on(current_cpu(), mp->m_inodegc_wq, &gc->work, + queue_delay); put_cpu_ptr(gc);
if (xfs_inodegc_want_flush_work(ip, items, shrinker_hits)) { @@ -2096,7 +2097,8 @@ xfs_inodegc_cpu_dead(
if (xfs_is_inodegc_enabled(mp)) { trace_xfs_inodegc_queue(mp, __return_address); - mod_delayed_work(mp->m_inodegc_wq, &gc->work, 0); + mod_delayed_work_on(current_cpu(), mp->m_inodegc_wq, &gc->work, + 0); } put_cpu_ptr(gc); }