From: Steven Rostedt Date: Fri, 24 Jul 2026 23:32:10 +0000 (-0400) Subject: tracing: perf: Fix stale head for perf syscall tracing X-Git-Tag: v7.2-rc5~8^2 X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=2c2b322acdcc78575b8d6afa64a085cf92e03c12;p=thirdparty%2Fkernel%2Flinux.git tracing: perf: Fix stale head for perf syscall tracing The code that can read the user space parameters of a system call may enable preemption and migrate. The head of the per CPU perf events list may be pointing to the wrong CPU event if the code migrates the task. Reassign the head pointer if the system call event called the code that may have caused a migration. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260724193210.03fae1d6@gandalf.local.home Reported-by: Sashiko <> Link: https://sashiko.dev/#/patchset/20260717173252.3431565-1-usama.arif%40linux.dev Fixes: edca33a56297d ("tracing: Fix failure to read user space from system call trace events") Signed-off-by: Steven Rostedt --- diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c index e98ee7e1e66f..8a4f3c75e39f 100644 --- a/kernel/trace/trace_syscalls.c +++ b/kernel/trace/trace_syscalls.c @@ -1451,6 +1451,11 @@ static void perf_syscall_enter(void *ignore, struct pt_regs *regs, long id) if (syscall_get_data(sys_data, args, &user_ptr, &size, user_sizes, &uargs, buf_size) < 0) return; + + /* The above may have caused a migration */ + head = this_cpu_ptr(sys_data->enter_event->perf_events); + if (hlist_empty(head)) + return; } /* get the size after alignment with the u32 buffer size field */