x86,preempt: Fix preemption for i386
Many people reported preemption/reschedule problems with i386 kernels
for .13 and .14. After Michele bisected this to a combination of
3e8e42c69bb ("sched: Revert need_resched() to look at TIF_NEED_RESCHED")
ded79754754 ("irq: Force hardirq exit's softirq processing on its own stack")
it finally dawned on me that i386's current_thread_info() was to
blame.
When we are on interrupt/exception stacks, we fail to observe the
right TIF_NEED_RESCHED bit and therefore the PREEMPT_NEED_RESCHED
folding malfunctions.
Current upstream fixes this by making i386 behave the same as x86_64
already did:
2432e1364bbe ("x86: Nuke the supervisor_stack field in i386 thread_info")
b807902a88c4 ("x86: Nuke GET_THREAD_INFO_WITH_ESP() macro for i386")
0788aa6a23cb ("x86: Prepare removal of previous_esp from i386 thread_info structure")
198d208df437 ("x86: Keep thread_info on thread stack in x86_32")
However, that is far too much to stuff into -stable. Therefore I
propose we merge the below patch which uses task_thread_info(current)
for tif_need_resched() instead of the ESP based current_thread_info().
This makes sure we always observe the one true TIF_NEED_RESCHED bit
and things will work as expected again.
Cc: fweisbec@gmail.com
Cc: mingo@kernel.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: David Cohen <david.a.cohen@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Tested-by: Stefan Bader <stefan.bader@canonical.com>
Tested-by: Toralf Förster <toralf.foerster@gmx.de>
Tested-by: Michele Ballabio <barra_cuda@katamail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
3 files changed
