On 3/16/21 12:45 PM, Steven Rostedt wrote:
On Tue, 16 Mar 2021 12:10:46 -0700 Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:From: Alexei Starovoitov <ast@xxxxxxxxxx> The following sequence of commands: register_ftrace_direct(ip, addr1); modify_ftrace_direct(ip, addr1, addr2); unregister_ftrace_direct(ip, addr2); will cause the kernel to warn: [ 30.179191] WARNING: CPU: 2 PID: 1961 at kernel/trace/ftrace.c:5223 unregister_ftrace_direct+0x130/0x150 [ 30.180556] CPU: 2 PID: 1961 Comm: test_progs W O 5.12.0-rc2-00378-g86bc10a0a711-dirty #3246 [ 30.182453] RIP: 0010:unregister_ftrace_direct+0x130/0x150 When modify_ftrace_direct() changes the addr from old to new it should update the addr stored in ftrace_direct_funcs. Otherwise the final unregister_ftrace_direct() won't find the address and will cause the splat. Fixes: 0567d6809182 ("ftrace: Add modify_ftrace_direct()") Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> --- Steven, I think I've changed it the way you requested. Please ack if so.The changes look fine, but I just found another issue that needs to be handled as well.@@ -5329,6 +5339,7 @@ int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry, int modify_ftrace_direct(unsigned long ip, unsigned long old_addr, unsigned long new_addr) { + struct ftrace_direct_func *direct, *new_direct; struct ftrace_func_entry *entry; struct dyn_ftrace *rec; int ret = -ENODEV; @@ -5344,6 +5355,20 @@ int modify_ftrace_direct(unsigned long ip, if (entry->direct != old_addr) goto out_unlock;+ direct = ftrace_find_direct_func(old_addr);+ if (WARN_ON(!direct)) + goto out_unlock; + if (direct->count > 1) { + ret = -ENOMEM; + new_direct = ftrace_alloc_direct_func(new_addr); + if (!new_direct) + goto out_unlock; + direct->count--; + new_direct->count++; + } else { + direct->addr = new_addr; + } + /* * If there's no other ftrace callback on the rec->ip location, * then it can be changed directly by the architecture.Everything looks good above, but then looking below this code we have: if (ftrace_rec_count(rec) == 1) { ret = ftrace_modify_direct_caller(entry, rec, old_addr, new_addr); } else { entry->direct = new_addr; ret = 0; } Where if ftrace_modify_direct_caller() fails, you need to put back the direct descriptors to where they were. struct ftrace_direct_func *new_direct = NULL; [..] if (unlikely(ret && new_direct)) { direct->count++; list_del_rcu(&new_direct->next); synchronize_rcu_tasks(); kfree(new_direct); } The above is highly unlikely to happen, but it could.
Sure. Will respin.
