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Subject[PATCH v3 09/14] 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>
Acked-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Anton Arapov <arapov@gmail.com>
Tested-by: Pratyush Anand <panand@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 93d939c..7e61c8c 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1511,6 +1511,16 @@ 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, 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;
@@ -1541,6 +1551,9 @@ static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
if (orig_ret_vaddr == -1)
goto fail;

+ /* drop the entries invalidated by longjmp() */
+ cleanup_return_instances(utask, regs);
+
/*
* We don't want to keep trampoline address in stack, rather keep the
* original return address of first caller thru all the consequent
--
1.5.5.1


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