84 lines
2.6 KiB
Diff
84 lines
2.6 KiB
Diff
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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
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Subject: [PATCH 07/31] mm: allow PF_MEMALLOC from softirq context
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Patch-mainline: not yet
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This is needed to allow network softirq packet processing to make use of
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PF_MEMALLOC.
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Currently softirq context cannot use PF_MEMALLOC due to it not being associated
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with a task, and therefore not having task flags to fiddle with - thus the gfp
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to alloc flag mapping ignores the task flags when in interrupts (hard or soft)
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context.
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Allowing softirqs to make use of PF_MEMALLOC therefore requires some trickery.
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We basically borrow the task flags from whatever process happens to be
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preempted by the softirq.
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So we modify the gfp to alloc flags mapping to not exclude task flags in
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softirq context, and modify the softirq code to save, clear and restore the
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PF_MEMALLOC flag.
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The save and clear, ensures the preempted task's PF_MEMALLOC flag doesn't
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leak into the softirq. The restore ensures a softirq's PF_MEMALLOC flag cannot
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leak back into the preempted process.
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Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
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Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
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---
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include/linux/sched.h | 7 +++++++
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kernel/softirq.c | 3 +++
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mm/page_alloc.c | 7 ++++---
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3 files changed, 14 insertions(+), 3 deletions(-)
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--- a/include/linux/sched.h
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+++ b/include/linux/sched.h
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@@ -1772,6 +1772,13 @@ static inline void rcu_copy_process(stru
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#endif
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+static inline void tsk_restore_flags(struct task_struct *p,
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+ unsigned long pflags, unsigned long mask)
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+{
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+ p->flags &= ~mask;
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+ p->flags |= pflags & mask;
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+}
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+
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#ifdef CONFIG_SMP
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extern int set_cpus_allowed_ptr(struct task_struct *p,
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const struct cpumask *new_mask);
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--- a/kernel/softirq.c
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+++ b/kernel/softirq.c
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@@ -194,6 +194,8 @@ asmlinkage void __do_softirq(void)
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__u32 pending;
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int max_restart = MAX_SOFTIRQ_RESTART;
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int cpu;
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+ unsigned long pflags = current->flags;
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+ current->flags &= ~PF_MEMALLOC;
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pending = local_softirq_pending();
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account_system_vtime(current);
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@@ -246,6 +248,7 @@ restart:
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account_system_vtime(current);
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_local_bh_enable();
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+ tsk_restore_flags(current, pflags, PF_MEMALLOC);
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}
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#ifndef __ARCH_HAS_DO_SOFTIRQ
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--- a/mm/page_alloc.c
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+++ b/mm/page_alloc.c
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@@ -1785,9 +1785,10 @@ int gfp_to_alloc_flags(gfp_t gfp_mask)
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alloc_flags |= ALLOC_HARDER;
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if (likely(!(gfp_mask & __GFP_NOMEMALLOC))) {
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- if (!in_interrupt() &&
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- ((p->flags & PF_MEMALLOC) ||
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- unlikely(test_thread_flag(TIF_MEMDIE))))
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+ if (!in_irq() && (p->flags & PF_MEMALLOC))
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+ alloc_flags |= ALLOC_NO_WATERMARKS;
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+ else if (!in_interrupt() &&
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+ unlikely(test_thread_flag(TIF_MEMDIE)))
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alloc_flags |= ALLOC_NO_WATERMARKS;
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}
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