On Fri, 27 Oct 2023 18:36:40 -0400 Steven Rostedt rostedt@goodmis.org wrote:
On Fri, 27 Oct 2023 12:20:11 -0700 Beau Belgrave beaub@linux.microsoft.com wrote:
On Fri, Oct 27, 2023 at 05:38:41PM +0530, Naresh Kamboju wrote:
Following kernel crash noticed on x86_64 while running selftests: user_events: ftrace_test running 6.6.0-rc7-next-20231026.
Reported-by: Linux Kernel Functional Testing lkft@linaro.org
kselftest: Running tests in user_events TAP version 13 1..4 # timeout set to 90 # selftests: user_events: ftrace_test [ 2391.606817] general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b8a83: 0000 [#1] PREEMPT SMP PTI [ 2391.617519] CPU: 1 PID: 34662 Comm: ftrace_test Not tainted 6.6.0-rc7-next-20231026 #1 [ 2391.625428] Hardware name: Supermicro SYS-5019S-ML/X11SSH-F, BIOS 2.7 12/07/2021 [ 2391.632811] RIP: 0010:tracing_update_buffers (kernel/trace/trace.c:6470) [ 2391.637952] Code: 90 90 90 90 90 90 90 90 90 90 90 90 66 0f 1f 00 55 31 f6 48 89 e5 41 55 41 54 53 48 89 fb 48 c7 c7 40 8c 61 94 e8 92 d3 5a 01 <44> 0f b6 a3 18 1f 00 00 41 80 fc 01 0f 87 c8 dc 4e 01 45 31
Warning is from this code: static void __trace_array_put(struct trace_array *this_tr) { WARN_ON(!this_tr->ref); this_tr->ref--; }
It seems like there might be a timing window or an incorrect call to trace_array_put() somewhere. Do you think this is related to the eventfs work?
No, I think this is was probably introduced by:
a1f157c7a3bb ("tracing: Expand all ring buffers individually")
Or possibly a mixture of the two changes? But anyway I think I need to look at this one first.
Not sure if the bug Beau hit is the same as this one, but the one Beau hit I think is fixed by this:
-- Steve
diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 4d2da7480e5f..4a54493b8419 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -234,6 +234,10 @@ create_file_dentry(struct eventfs_inode *ei, struct dentry **e_dentry, bool invalidate = false;
mutex_lock(&eventfs_mutex); + if (ei->is_freed) { + mutex_unlock(&eventfs_mutex); + return NULL; + } /* If the e_dentry already has a dentry, use it */ if (*e_dentry) { /* lookup does not need to up the ref count */