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Date: Mon, 7 Feb 2022 15:57:18 +0100 From: Frederic Weisbecker <frederic@...nel.org> To: Marcelo Tosatti <mtosatti@...hat.com> Cc: linux-kernel@...r.kernel.org, Nitesh Lal <nilal@...hat.com>, Nicolas Saenz Julienne <nsaenzju@...hat.com>, Christoph Lameter <cl@...ux.com>, Juri Lelli <juri.lelli@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Alex Belits <abelits@...its.com>, Peter Xu <peterx@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, Daniel Bristot de Oliveira <bristot@...hat.com>, Oscar Shiang <oscar0225@...email.tw> Subject: Re: [patch v11 05/13] task isolation: sync vmstats on return to userspace On Fri, Feb 04, 2022 at 02:35:42PM -0300, Marcelo Tosatti wrote: > The logic to disable vmstat worker thread, when entering > nohz full, does not cover all scenarios. For example, it is possible > for the following to happen: > > 1) enter nohz_full, which calls refresh_cpu_vm_stats, syncing the stats. > 2) app runs mlock, which increases counters for mlock'ed pages. > 3) start -RT loop > > Since refresh_cpu_vm_stats from nohz_full logic can happen _before_ > the mlock, vmstat shepherd can restart vmstat worker thread on > the CPU in question. > > To fix this, use the task isolation prctl interface to quiesce > deferred actions when returning to userspace. > > This patch adds hooks to fork and exit code paths. > > Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com> > > --- > v11: fold patch to add task_isol_exit hooks (Frederic) > Use _TIF_TASK_ISOL bit on thread flags (Frederic) > > v6: modify exit_to_user_mode_loop to cover exceptions and interrupts > v5: no changes > v4: add oneshot mode support > > include/linux/task_isolation.h | 16 ++++++++++++++++ > include/linux/vmstat.h | 8 ++++++++ > kernel/entry/common.c | 15 +++++++++++---- > kernel/task_isolation.c | 21 +++++++++++++++++++++ > mm/vmstat.c | 21 +++++++++++++++++++++ > 5 files changed, 77 insertions(+), 4 deletions(-) > > Index: linux-2.6/include/linux/task_isolation.h > =================================================================== > --- linux-2.6.orig/include/linux/task_isolation.h > +++ linux-2.6/include/linux/task_isolation.h > @@ -27,6 +27,13 @@ static inline void task_isol_free(struct > __task_isol_free(tsk); > } > > +void __task_isol_exit(struct task_struct *tsk); > +static inline void task_isol_exit(struct task_struct *tsk) > +{ > + if (tsk->task_isol_info) > + __task_isol_exit(tsk); > +} > + > int prctl_task_isol_feat_get(unsigned long arg2, unsigned long arg3, > unsigned long arg4, unsigned long arg5); > int prctl_task_isol_cfg_get(unsigned long arg2, unsigned long arg3, > @@ -40,12 +47,22 @@ int prctl_task_isol_activate_set(unsigne > > int __copy_task_isol(struct task_struct *tsk); > > +void task_isol_exit_to_user_mode(void); > + > #else > > +static inline void task_isol_exit_to_user_mode(void) > +{ > +} > + > static inline void task_isol_free(struct task_struct *tsk) > { > } > > +static inline void task_isol_exit(struct task_struct *tsk) > +{ > +} > + > static inline int prctl_task_isol_feat_get(unsigned long arg2, > unsigned long arg3, > unsigned long arg4, > Index: linux-2.6/include/linux/vmstat.h > =================================================================== > --- linux-2.6.orig/include/linux/vmstat.h > +++ linux-2.6/include/linux/vmstat.h > @@ -21,6 +21,14 @@ int sysctl_vm_numa_stat_handler(struct c > void *buffer, size_t *length, loff_t *ppos); > #endif > > +#if defined(CONFIG_SMP) && defined(CONFIG_TASK_ISOLATION) > +void sync_vmstat(void); > +#else > +static inline void sync_vmstat(void) > +{ > +} > +#endif > + > struct reclaim_stat { > unsigned nr_dirty; > unsigned nr_unqueued_dirty; > Index: linux-2.6/kernel/entry/common.c > =================================================================== > --- linux-2.6.orig/kernel/entry/common.c > +++ linux-2.6/kernel/entry/common.c > @@ -6,6 +6,7 @@ > #include <linux/livepatch.h> > #include <linux/audit.h> > #include <linux/tick.h> > +#include <linux/task_isolation.h> > > #include "common.h" > > @@ -174,6 +175,9 @@ static unsigned long exit_to_user_mode_l > if (ti_work & _TIF_NOTIFY_RESUME) > tracehook_notify_resume(regs); > > + if (ti_work & _TIF_TASK_ISOL) > + task_isol_exit_to_user_mode(); > + > /* Architecture specific TIF work */ > arch_exit_to_user_mode_work(regs, ti_work); > > Index: linux-2.6/kernel/task_isolation.c > =================================================================== > --- linux-2.6.orig/kernel/task_isolation.c > +++ linux-2.6/kernel/task_isolation.c > @@ -18,6 +18,12 @@ > #include <linux/sysfs.h> > #include <linux/init.h> > #include <linux/sched/task.h> > +#include <linux/mm.h> > +#include <linux/vmstat.h> > + > +void __task_isol_exit(struct task_struct *tsk) > +{ > +} > > void __task_isol_free(struct task_struct *tsk) > { > @@ -251,6 +257,9 @@ static int cfg_feat_quiesce_set(unsigned > task_isol_info->quiesce_mask = i_qctrl->quiesce_mask; > task_isol_info->oneshot_mask = i_qctrl->quiesce_oneshot_mask; > task_isol_info->conf_mask |= ISOL_F_QUIESCE; > + if (task_isol_info->quiesce_mask & ISOL_F_QUIESCE_VMSTATS) > + set_thread_flag(TIF_TASK_ISOL); Should you check if (i->active_mask == ISOL_F_QUIESCE) before setting the flag? > + > ret = 0; > > out_free: > @@ -303,6 +312,7 @@ int __copy_task_isol(struct task_struct > new_info->active_mask = info->active_mask; > > tsk->task_isol_info = new_info; > + set_ti_thread_flag(task_thread_info(tsk), TIF_TASK_ISOL); Same here? > > return 0; Thanks.
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