On Tue, 2020-03-03 at 14:39 -0600, Tom Zanussi wrote: > Hi Scott, > > On Tue, 2020-03-03 at 13:56 -0600, Scott Wood wrote: > > On Thu, 2020-02-27 at 08:33 -0600, zanussi@xxxxxxxxxx wrote: > > > From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > > > > > > v4.14.170-rt75-rc2 stable review patch. > > > If anyone has any objections, please let me know. > > > > > > ----------- > > > > > > > > > [ Upstream commit 140d7f54a5fff02898d2ca9802b39548bf7455f1 ] > > > > > > If user task changes the CPU affinity mask of a running task it > > > will > > > dispatch migration request if the current CPU is no longer allowed. > > > This > > > might happen shortly before a task enters a migrate_disable() > > > section. > > > Upon leaving the migrate_disable() section, the task will notice > > > that > > > the current CPU is no longer allowed and will will dispatch its own > > > migration request to move it off the current CPU. > > > While invoking __schedule() the first migration request will be > > > processed and the task returns on the "new" CPU with "arg.done = > > > 0". Its > > > own migration request will be processed shortly after and will > > > result in > > > memory corruption if the stack memory, designed for request, was > > > used > > > otherwise in the meantime. > > > > > > Spin until the migration request has been processed if it was > > > accepted. > > > > > > Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> > > > Signed-off-by: Tom Zanussi <zanussi@xxxxxxxxxx> > > > --- > > > kernel/sched/core.c | 7 +++++-- > > > 1 file changed, 5 insertions(+), 2 deletions(-) > > > > As I said in https://marc.info/?l=linux-rt-users&m=158258256415340&w= > > 2 if > > you take thhis you should take the followup 2dcd94b443c5dcbc ("sched: > > migrate_enable: Use per-cpu cpu_stop_work") > > > > Yes, I didn't forget about this, it's just that I can't apply this to > 4.14-rt until 4.19-rt does, otherwise it will be seen as a regression > to someone moving from 4.14-rt to 4.19-rt. > > I will be keeping my eye out for when that happens and will apply it to > the next backport release at that point. > > Thanks for making sure it wasn't missed in any case. Steven, any plans to merge that patch into 4.19-rt? In the meantime, I guess it's a question of whether the bug fixed by patch 18/23 is worse than the (probably quite hard to hit) deadlock addressed by 2dcd94b443c5dcbc. -Scott
