src/patches/suse-2.6.27.25/patches.suse/SoN-10-mm-PF_MEMALLOC-softirq.patch

   1 From: Peter Zijlstra <a.p.zijlstra@chello.nl>
   2 Subject: mm: allow PF_MEMALLOC from softirq context
   3 Patch-mainline: No
   4 References: FATE#303834
   5
   6 This is needed to allow network softirq packet processing to make use of
   7 PF_MEMALLOC.
   8
   9 Currently softirq context cannot use PF_MEMALLOC due to it not being associated
  10 with a task, and therefore not having task flags to fiddle with - thus the gfp
  11 to alloc flag mapping ignores the task flags when in interrupts (hard or soft)
  12 context.
  13
  14 Allowing softirqs to make use of PF_MEMALLOC therefore requires some trickery.
  15 We basically borrow the task flags from whatever process happens to be
  16 preempted by the softirq.
  17
  18 So we modify the gfp to alloc flags mapping to not exclude task flags in
  19 softirq context, and modify the softirq code to save, clear and restore the
  20 PF_MEMALLOC flag.
  21
  22 The save and clear, ensures the preempted task's PF_MEMALLOC flag doesn't
  23 leak into the softirq. The restore ensures a softirq's PF_MEMALLOC flag cannot
  24 leak back into the preempted process.
  25
  26 Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
  27 Acked-by: Neil Brown <neilb@suse.de>
  28 Acked-by: Suresh Jayaraman <sjayaraman@suse.de>
  29
  30 ---
  31  include/linux/sched.h |    7 +++++++
  32  kernel/softirq.c      |    3 +++
  33  mm/page_alloc.c       |    7 ++++---
  34  3 files changed, 14 insertions(+), 3 deletions(-)
  35
  36 --- a/include/linux/sched.h
  37 +++ b/include/linux/sched.h
  38 @@ -1554,6 +1554,13 @@ extern cputime_t task_gtime(struct task_
  39  #define tsk_used_math(p) ((p)->flags & PF_USED_MATH)
  40  #define used_math() tsk_used_math(current)
  41
  42 +static inline void tsk_restore_flags(struct task_struct *p,
  43 +                                    unsigned long pflags, unsigned long mask)
  44 +{
  45 +       p->flags &= ~mask;
  46 +       p->flags |= pflags & mask;
  47 +}
  48 +
  49  #ifdef CONFIG_SMP
  50  extern int set_cpus_allowed_ptr(struct task_struct *p,
  51                                 const cpumask_t *new_mask);
  52 --- a/kernel/softirq.c
  53 +++ b/kernel/softirq.c
  54 @@ -188,6 +188,8 @@ asmlinkage void __do_softirq(void)
  55         __u32 pending;
  56         int max_restart = MAX_SOFTIRQ_RESTART;
  57         int cpu;
  58 +       unsigned long pflags = current->flags;
  59 +       current->flags &= ~PF_MEMALLOC;
  60
  61         pending = local_softirq_pending();
  62         account_system_vtime(current);
  63 @@ -228,6 +230,7 @@ restart:
  64
  65         account_system_vtime(current);
  66         _local_bh_enable();
  67 +       tsk_restore_flags(current, pflags, PF_MEMALLOC);
  68  }
  69
  70  #ifndef __ARCH_HAS_DO_SOFTIRQ
  71 --- a/mm/page_alloc.c
  72 +++ b/mm/page_alloc.c
  73 @@ -1478,9 +1478,10 @@ int gfp_to_alloc_flags(gfp_t gfp_mask)
  74                 alloc_flags |= ALLOC_HARDER;
  75
  76         if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
  77 -               if (!in_interrupt() &&
  78 -                   ((p->flags & PF_MEMALLOC) ||
  79 -                    unlikely(test_thread_flag(TIF_MEMDIE))))
  80 +               if (!in_irq() && (p->flags & PF_MEMALLOC))
  81 +                       alloc_flags |= ALLOC_NO_WATERMARKS;
  82 +               else if (!in_interrupt() &&
  83 +                               unlikely(test_thread_flag(TIF_MEMDIE)))
  84                         alloc_flags |= ALLOC_NO_WATERMARKS;
  85         }
  86