On 03/03/2022 15.12, Sebastian Andrzej Siewior wrote:
On 2022-03-03 14:59:47 [+0100], Toke Høiland-Jørgensen wrote:
Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> writes:
Since the commit mentioned below __xdp_reg_mem_model() can return a NULL
pointer. This pointer is dereferenced in trace_mem_connect() which leads
to segfault. It can be reproduced with enabled trace events during ifup.
Only assign the arguments in the trace-event macro if `xa' is set.
Otherwise set the parameters to 0.
Fixes: 4a48ef70b93b8 ("xdp: Allow registering memory model without rxq reference")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Hmm, so before the commit you mention, the tracepoint wasn't triggered
at all in the code path that now sets xdp_alloc is NULL. So I'm
wondering if we should just do the same here? Is the trace event useful
in all cases?
Correct. It says:
| ip-1230 [003] ..... 3.053473: mem_connect: mem_id=0 mem_type=PAGE_SHARED allocator=0000000000000000 ifindex=2
Alternatively, if we keep it, I think the mem.id and mem.type should be
available from rxq->mem, right?
Yes, if these are the same things. In my case they are also 0:
| ip-1245 [000] ..... 3.045684: mem_connect: mem_id=0 mem_type=PAGE_SHARED allocator=0000000000000000 ifindex=2
| ifconfig-1332 [003] ..... 21.030879: mem_connect: mem_id=0 mem_type=PAGE_SHARED allocator=0000000000000000 ifindex=3
So depends on what makes sense that tp can be skipped for xa == NULL or
remain with
__entry->mem_id = rxq->mem.id;
__entry->mem_type = rxq->mem.type;
__entry->allocator = xa ? xa->allocator : NULL;
if it makes sense.
I have two bpftrace scripts [1] and [2] that use this tracepoint.
It is scripts to help driver developers detect memory leaks when using
page_pool from their drivers.
I'm a little pressured on time, so I've not evaluated if your change
makes sense.
In the scripts I do use both mem.id and mem.type.
[1]
https://github.com/xdp-project/xdp-project/blob/master/areas/mem/bpftrace/xdp_mem_track01.bt
[2]
https://github.com/xdp-project/xdp-project/blob/master/areas/mem/bpftrace/xdp_mem_track02.bt
--Jesper
