Re: [syzbot] possible deadlock in trie_delete_elem

syzbot
2024-06-06T14:04:05Z

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: possible deadlock in trie_delete_elem
Author: norkam41@gmail.com

#syz test: https://linux.googlesource.com/linux/kernel/git/torvalds/linux e377d803b65ee4130213b3c041fc25fdfec1bd90

---
kernel/trace/bpf_trace.c | 13 +++++++++++--
kernel/tracepoint.c | 15 +++++++++++++--
2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 2d29bc0f21cc..75fdb8e3abaa 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -2393,12 +2393,21 @@ void __bpf_trace_run(struct bpf_raw_tp_link *link, u64 *args)
cant_sleep();

// return if instrumentation disabled, see: bpf_disable_instrumentation
- if (unlikely(__this_cpu_read(bpf_prog_active))) {
+ int instrumentation = unlikely(__this_cpu_read(bpf_prog_active));
+ if (instrumentation) {
+ printk("SKIP FOR INSTRUMENTATION: %s > %s > %p /%i ==============\n",
+ prog->aux->name,
+ link->btp->tp->name, prog, instrumentation);
bpf_prog_inc_misses_counter(prog);
return;
}

- if (unlikely(this_cpu_inc_return(*(prog->active)) != 1)) {
+ int active = this_cpu_inc_return(*(prog->active));
+ // printk("%s > %s > %p /%i\n", prog->aux->name, link->btp->tp->name, prog, active);
+ if (active != 1) {
+ printk("SKIP FOR ACTIVE: %s > %s > %p /%i =======================\n",
+ prog->aux->name,
+ link->btp->tp->name, prog, active);
bpf_prog_inc_misses_counter(prog);
goto out;
}
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 8d1507dd0724..a0a0d8b16b41 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -168,12 +168,21 @@ static inline void release_probes(struct tracepoint_func *old)
static void debug_print_probes(struct tracepoint_func *funcs)
{
int i;
+ struct bpf_raw_tp_link *link;

if (!tracepoint_debug || !funcs)
return;

- for (i = 0; funcs[i].func; i++)
- printk(KERN_DEBUG "Probe %d : %p\n", i, funcs[i].func);
+ for (i = 0; funcs[i].func; i++) {
+ link = funcs[i].data;
+ int active = this_cpu_read(*(link->link.prog->active));
+ printk("Probe %d : %p / %p: %s/%d / %i\n", i,
+ funcs[i].func,
+ link,
+ link->link.prog->aux->name,
+ active,
+ funcs[i].prio);
+ }
}

static struct tracepoint_func *
@@ -298,6 +307,8 @@ static enum tp_func_state nr_func_state(const struct tracepoint_func *tp_funcs)
{
if (!tp_funcs)
return TP_FUNC_0;
+ if (!tp_funcs[0].func)
+ return TP_FUNC_0;
if (!tp_funcs[1].func)
return TP_FUNC_1;
if (!tp_funcs[2].func)
--
2.34.1