projects / people / teissler / ipfire-2.x.git / blame
| Commit | Line | Data |
|---|---|---|
| 00e5a55c BS |
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 |