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authorSong Liu <songliubraving@fb.com>2018-05-07 10:50:48 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2018-05-14 23:29:45 +0200
commitbae77c5eb5b2107e300fb02da2311f2aa0d8ee3c (patch)
tree54161e53098e6b684e7eb03bab0082626f0307fe /kernel/bpf/stackmap.c
parenta84880ef4352c61896028448d809e32f8646628d (diff)
bpf: enable stackmap with build_id in nmi context
Currently, we cannot parse build_id in nmi context because of up_read(&current->mm->mmap_sem), this makes stackmap with build_id less useful. This patch enables parsing build_id in nmi by putting the up_read() call in irq_work. To avoid memory allocation in nmi context, we use per cpu variable for the irq_work. As a result, only one irq_work per cpu is allowed. If the irq_work is in-use, we fallback to only report ips. Cc: Alexei Starovoitov <ast@kernel.org> Cc: Daniel Borkmann <daniel@iogearbox.net> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Song Liu <songliubraving@fb.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Diffstat (limited to 'kernel/bpf/stackmap.c')
-rw-r--r--kernel/bpf/stackmap.c59
1 files changed, 53 insertions, 6 deletions
diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 3ba102b41512..b59ace0f0f09 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c
@@ -11,6 +11,7 @@
#include <linux/perf_event.h>
#include <linux/elf.h>
#include <linux/pagemap.h>
+#include <linux/irq_work.h>
#include "percpu_freelist.h"
#define STACK_CREATE_FLAG_MASK \
@@ -32,6 +33,23 @@ struct bpf_stack_map {
struct stack_map_bucket *buckets[];
};
+/* irq_work to run up_read() for build_id lookup in nmi context */
+struct stack_map_irq_work {
+ struct irq_work irq_work;
+ struct rw_semaphore *sem;
+};
+
+static void do_up_read(struct irq_work *entry)
+{
+ struct stack_map_irq_work *work;
+
+ work = container_of(entry, struct stack_map_irq_work, irq_work);
+ up_read(work->sem);
+ work->sem = NULL;
+}
+
+static DEFINE_PER_CPU(struct stack_map_irq_work, up_read_work);
+
static inline bool stack_map_use_build_id(struct bpf_map *map)
{
return (map->map_flags & BPF_F_STACK_BUILD_ID);
@@ -267,17 +285,27 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
{
int i;
struct vm_area_struct *vma;
+ bool in_nmi_ctx = in_nmi();
+ bool irq_work_busy = false;
+ struct stack_map_irq_work *work;
+
+ if (in_nmi_ctx) {
+ work = this_cpu_ptr(&up_read_work);
+ if (work->irq_work.flags & IRQ_WORK_BUSY)
+ /* cannot queue more up_read, fallback */
+ irq_work_busy = true;
+ }
/*
- * We cannot do up_read() in nmi context, so build_id lookup is
- * only supported for non-nmi events. If at some point, it is
- * possible to run find_vma() without taking the semaphore, we
- * would like to allow build_id lookup in nmi context.
+ * We cannot do up_read() in nmi context. To do build_id lookup
+ * in nmi context, we need to run up_read() in irq_work. We use
+ * a percpu variable to do the irq_work. If the irq_work is
+ * already used by another lookup, we fall back to report ips.
*
* Same fallback is used for kernel stack (!user) on a stackmap
* with build_id.
*/
- if (!user || !current || !current->mm || in_nmi() ||
+ if (!user || !current || !current->mm || irq_work_busy ||
down_read_trylock(&current->mm->mmap_sem) == 0) {
/* cannot access current->mm, fall back to ips */
for (i = 0; i < trace_nr; i++) {
@@ -299,7 +327,13 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs,
- vma->vm_start;
id_offs[i].status = BPF_STACK_BUILD_ID_VALID;
}
- up_read(&current->mm->mmap_sem);
+
+ if (!in_nmi_ctx) {
+ up_read(&current->mm->mmap_sem);
+ } else {
+ work->sem = &current->mm->mmap_sem;
+ irq_work_queue(&work->irq_work);
+ }
}
BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map,
@@ -575,3 +609,16 @@ const struct bpf_map_ops stack_map_ops = {
.map_update_elem = stack_map_update_elem,
.map_delete_elem = stack_map_delete_elem,
};
+
+static int __init stack_map_init(void)
+{
+ int cpu;
+ struct stack_map_irq_work *work;
+
+ for_each_possible_cpu(cpu) {
+ work = per_cpu_ptr(&up_read_work, cpu);
+ init_irq_work(&work->irq_work, do_up_read);
+ }
+ return 0;
+}
+subsys_initcall(stack_map_init);