On Mon, 16 Nov 2020 17:51:07 -0500 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > [ Kees, I added you because you tend to know about these things. > Is it OK to assign a void func(void) that doesn't do anything and returns > nothing to a function pointer that could be call with parameters? We need > to add stubs for tracepoints when we fail to allocate a new array on > removal of a callback, but the callbacks do have arguments, but the stub > called does not have arguments. > > Matt, Does this patch fix the error your patch was trying to fix? > ] > > The list of tracepoint callbacks is managed by an array that is protected > by RCU. To update this array, a new array is allocated, the updates are > copied over to the new array, and then the list of functions for the > tracepoint is switched over to the new array. After a completion of an RCU > grace period, the old array is freed. > > This process happens for both adding a callback as well as removing one. > But on removing a callback, if the new array fails to be allocated, the > callback is not removed, and may be used after it is freed by the clients > of the tracepoint. > > There's really no reason to fail if the allocation for a new array fails > when removing a function. Instead, the function can simply be replaced by a > stub function that could be cleaned up on the next modification of the > array. That is, instead of calling the function registered to the > tracepoint, it would call a stub function in its place. > > Link: https://lore.kernel.org/r/20201115055256.65625-1-mmullins@xxxxxxx > > Cc: stable@xxxxxxxxxxxxxxx > Fixes: 97e1c18e8d17b ("tracing: Kernel Tracepoints") > Reported-by: syzbot+83aa762ef23b6f0d1991@xxxxxxxxxxxxxxxxxxxxxxxxx > Reported-by: syzbot+d29e58bb557324e55e5e@xxxxxxxxxxxxxxxxxxxxxxxxx > Reported-by: Matt Mullins <mmullins@xxxxxxx> Forgot my: Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> and tested with adding this (just to see if paths are hit). -- Steve diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c index 774b3733cbbe..96f081ff5284 100644 --- a/kernel/tracepoint.c +++ b/kernel/tracepoint.c @@ -167,6 +167,7 @@ func_add(struct tracepoint_func **funcs, struct tracepoint_func *tp_func, /* Need to copy one at a time to remove stubs */ int probes = 0; + printk("HERE stub_funcs=%d\n", stub_funcs); pos = -1; for (nr_probes = 0; old[nr_probes].func; nr_probes++) { if (old[nr_probes].func == tp_stub_func) @@ -235,7 +236,7 @@ static void *func_remove(struct tracepoint_func **funcs, int j = 0; /* N -> M, (N > 1, M > 0) */ /* + 1 for NULL */ - new = allocate_probes(nr_probes - nr_del + 1, __GFP_NOFAIL); + new = NULL; //allocate_probes(nr_probes - nr_del + 1, __GFP_NOFAIL); if (new) { for (i = 0; old[i].func; i++) if ((old[i].func != tp_func->func
