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Subject[PATCH 09/10] uprobes: Change prepare_uretprobe() to (try to) flush the dead frames
Change prepare_uretprobe() to flush the !arch_uretprobe_is_alive()
return_instance's. This is not needed correctness-wise, but can help
to avoid the failure caused by MAX_URETPROBE_DEPTH.

Note: in this case arch_uretprobe_is_alive() can be false positive,
the stack can grow after longjmp(). Unfortunately, the kernel can't
100% solve this problem, but see the next patch.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/uprobes.c | 13 +++++++++++++
1 files changed, 13 insertions(+), 0 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 0dd7ff7..b6433fb 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1522,6 +1522,16 @@ static unsigned long get_trampoline_vaddr(void)
return trampoline_vaddr;
}

+static void cleanup_return_instances(struct uprobe_task *utask, struct pt_regs *regs)
+{
+ struct return_instance *ri = utask->return_instances;
+ while (ri && !arch_uretprobe_is_alive(&ri->auret, regs)) {
+ ri = free_ret_instance(ri);
+ utask->depth--;
+ }
+ utask->return_instances = ri;
+}
+
static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
{
struct return_instance *ri;
@@ -1576,6 +1586,9 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
ri->orig_ret_vaddr = orig_ret_vaddr;
ri->chained = chained;

+ if (utask->depth) /* drop the entries invalidated by longjmp() */
+ cleanup_return_instances(utask, regs);
+
utask->depth++;
ri->next = utask->return_instances;
utask->return_instances = ri;
--
1.5.5.1


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