Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider: - [High] The panic handler unconditionally attempts to acquire a per-CPU reader spinlock that may be held by a CPU halted by smp_send_stop(), leading to a permanent deadlock during kernel panic. - [High] Missing touch_nmi_watchdog() in the panic dump loop can cause a secondary panic or hard reset. - [Medium] Mixing goto-based error handling with __free() scope-based cleanup in trace_remote_iter(). - [Low] Missing READ_ONCE() when reading remote->panic_on in dump_on_panic_show(). --
--- Patch [13]: [PATCH v6 13/18] tracing/remotes: Add dump_on_panic tracefs file --- commit 33a5774bde5e05c9ff209cc5026a9b962c22df16 Author: Vincent Donnefort <[email protected]> tracing/remotes: Add dump_on_panic tracefs file This commit adds a dump_on_panic tracefs file. When enabled, it dumps the content of the trace remote buffer to the console if the system panics. > diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c > index 9e78267d71f8b..5536e0df43795 100644 > --- a/kernel/trace/trace_remote.c > +++ b/kernel/trace/trace_remote.c [ ... ] > @@ -434,58 +455,68 @@ static void trace_remote_dec_poll(struct trace_remote > *remote) > static struct trace_remote_iterator > *trace_remote_iter(struct trace_remote *remote, int cpu, enum tri_type type) > { > - struct trace_remote_iterator *iter = NULL; > + struct trace_remote_iterator *iter __free(kfree) = kzalloc_obj(*iter); [Severity: Medium] This isn't a bug, but this function mixes scope-based cleanup (__free) with a goto-based error handling pattern. According to the cleanup subsystem guidelines, mixing goto-based cleanup labels and __free() declarations in the same function is forbidden because it creates confusing ownership semantics. Should this function either use goto-based cleanup exclusively, or be fully converted to scope-based cleanup? [ ... ] > @@ -989,6 +1024,117 @@ static int dmesg_show(struct seq_file *s, void *unused) > } > DEFINE_TRACE_REMOTE_ATTRIBUTE(dmesg); > > +static int trace_remote_panic_handler(struct notifier_block *self, unsigned > long ev, void *v) > +{ > + struct trace_remote *remote = container_of(self, struct trace_remote, > panic_notifier); > + struct trace_remote_iterator *iter = > smp_load_acquire(&remote->panic_iter); > + int cpu; > + > + if (!iter) { > + pr_warn("Unexpected error: no panic iterator for the trace > remote\n"); > + return NOTIFY_DONE; > + } > + > + for_each_possible_cpu(cpu) { > + if (iter->rb_iters[cpu]) { > + /* No RING_BUFFER_ALL_CPUS to avoid taking > cpu_read_lock() */ > + ring_buffer_read_remote_meta_page(remote->trace_buffer, > cpu); > + ring_buffer_iter_reset(iter->rb_iters[cpu]); > + } > + } [Severity: High] Can this loop deadlock indefinitely during a panic? If another CPU is actively reading the remote trace buffer and holds its reader_lock, the panic() function will stop that CPU via smp_send_stop(). When the panicking CPU executes this loop, ring_buffer_read_remote_meta_page() calls rb_reader_lock(). If in_nmi() is false (which happens on a normal oops or SysRq-C), rb_reader_lock() will unconditionally attempt to acquire the lock held by the stopped CPU rather than using a trylock. Will this cause the panic recovery process to hang forever? > + > + while (trace_remote_iter_read_event(iter)) { > + trace_seq_init(&iter->seq); > + > + trace_remote_iter_print_event(iter); > + trace_seq_putc(&iter->seq, 0); > + pr_emerg("%s", seq_buf_str(&iter->seq.seq)); > + > + trace_remote_iter_move(iter); > + } [Severity: High] Since serial consoles can be slow and remote trace buffers can contain many events, could the time spent in this printing loop trigger the NMI watchdog and cause a hard reset before the panic dump completes? Does this loop need a call to touch_nmi_watchdog()? > + > + return NOTIFY_DONE; > +} [ ... ] > +static int dump_on_panic_show(struct seq_file *s, void *unused) > +{ > + struct trace_remote *remote = s->private; > + > + seq_printf(s, "%d\n", remote->panic_on); [Severity: Low] Does this unprotected read of remote->panic_on need a READ_ONCE()? Since dump_on_panic_write() modifies this flag concurrently under remote->lock, this is formally a data race under the Linux kernel memory model and might be flagged by KCSAN. > + > + return 0; > +} -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=13
