The patch below does not apply to the 5.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y git checkout FETCH_HEAD git cherry-pick -x 5f1ef0dfcb5b7f4a91a9b0e0ba533efd9f7e2cdb # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2026011223-watch-majestic-5e5d@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 5f1ef0dfcb5b7f4a91a9b0e0ba533efd9f7e2cdb Mon Sep 17 00:00:00 2001 From: Steven Rostedt rostedt@goodmis.org Date: Mon, 5 Jan 2026 20:31:41 -0500 Subject: [PATCH] tracing: Add recursion protection in kernel stack trace recording
A bug was reported about an infinite recursion caused by tracing the rcu events with the kernel stack trace trigger enabled. The stack trace code called back into RCU which then called the stack trace again.
Expand the ftrace recursion protection to add a set of bits to protect events from recursion. Each bit represents the context that the event is in (normal, softirq, interrupt and NMI).
Have the stack trace code use the interrupt context to protect against recursion.
Note, the bug showed an issue in both the RCU code as well as the tracing stacktrace code. This only handles the tracing stack trace side of the bug. The RCU fix will be handled separately.
Link: https://lore.kernel.org/all/20260102122807.7025fc87@gandalf.local.home/
Cc: stable@vger.kernel.org Cc: Masami Hiramatsu mhiramat@kernel.org Cc: Mathieu Desnoyers mathieu.desnoyers@efficios.com Cc: Joel Fernandes joel@joelfernandes.org Cc: "Paul E. McKenney" paulmck@kernel.org Cc: Boqun Feng boqun.feng@gmail.com Link: https://patch.msgid.link/20260105203141.515cd49f@gandalf.local.home Reported-by: Yao Kai yaokai34@huawei.com Tested-by: Yao Kai yaokai34@huawei.com Fixes: 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in __rcu_read_unlock()") Signed-off-by: Steven Rostedt (Google) rostedt@goodmis.org
diff --git a/include/linux/trace_recursion.h b/include/linux/trace_recursion.h index ae04054a1be3..e6ca052b2a85 100644 --- a/include/linux/trace_recursion.h +++ b/include/linux/trace_recursion.h @@ -34,6 +34,13 @@ enum { TRACE_INTERNAL_SIRQ_BIT, TRACE_INTERNAL_TRANSITION_BIT,
+ /* Internal event use recursion bits */ + TRACE_INTERNAL_EVENT_BIT, + TRACE_INTERNAL_EVENT_NMI_BIT, + TRACE_INTERNAL_EVENT_IRQ_BIT, + TRACE_INTERNAL_EVENT_SIRQ_BIT, + TRACE_INTERNAL_EVENT_TRANSITION_BIT, + TRACE_BRANCH_BIT, /* * Abuse of the trace_recursion. @@ -58,6 +65,8 @@ enum {
#define TRACE_LIST_START TRACE_INTERNAL_BIT
+#define TRACE_EVENT_START TRACE_INTERNAL_EVENT_BIT + #define TRACE_CONTEXT_MASK ((1 << (TRACE_LIST_START + TRACE_CONTEXT_BITS)) - 1)
/* diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 6f2148df14d9..aef9058537d5 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3012,6 +3012,11 @@ static void __ftrace_trace_stack(struct trace_array *tr, struct ftrace_stack *fstack; struct stack_entry *entry; int stackidx; + int bit; + + bit = trace_test_and_set_recursion(_THIS_IP_, _RET_IP_, TRACE_EVENT_START); + if (bit < 0) + return;
/* * Add one, for this function and the call to save_stack_trace() @@ -3080,6 +3085,7 @@ static void __ftrace_trace_stack(struct trace_array *tr, /* Again, don't let gcc optimize things here */ barrier(); __this_cpu_dec(ftrace_stack_reserve); + trace_clear_recursion(bit); }
static inline void ftrace_trace_stack(struct trace_array *tr,