| Message ID | 20240826060718.267261-1-vmalik@redhat.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [v2] objpool: fix choosing allocation for percpu slots | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Mon, 26 Aug 2024 08:07:18 +0200 Viktor Malik <vmalik@redhat.com> wrote: > objpool intends to use vmalloc for default (non-atomic) allocations of > percpu slots and objects. However, the condition checking if GFP flags > are equal to GFP_ATOMIC is wrong b/c GFP_ATOMIC is a combination of bits > (__GFP_HIGH|__GFP_KSWAPD_RECLAIM) and so `pool->gfp & GFP_ATOMIC` will > be true if either bit is set. Since GFP_ATOMIC and GFP_KERNEL share the > ___GFP_KSWAPD_RECLAIM bit, kmalloc will be used in cases when GFP_KERNEL > is specified, i.e. in all current usages of objpool. > > This may lead to unexpected OOM errors since kmalloc cannot allocate > large amounts of memory. > > For instance, objpool is used by fprobe rethook which in turn is used by > BPF kretprobe.multi and kprobe.session probe types. Trying to attach > these to all kernel functions with libbpf using > > SEC("kprobe.session/*") > int kprobe(struct pt_regs *ctx) > { > [...] > } > > fails on objpool slot allocation with ENOMEM. > > Fix the condition to truly use vmalloc by default. > > Fixes: b4edb8d2d464 ("lib: objpool added: ring-array based lockless MPMC") > Signed-off-by: Viktor Malik <vmalik@redhat.com> > Acked-by: Andrii Nakryiko <andrii@kernel.org> > Reviewed-by: Matt Wu <wuqiang.matt@bytedance.com> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> -- Steve > --- > lib/objpool.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/lib/objpool.c b/lib/objpool.c > index 234f9d0bd081..fd108fe0d095 100644 > --- a/lib/objpool.c > +++ b/lib/objpool.c > @@ -76,7 +76,7 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs, > * mimimal size of vmalloc is one page since vmalloc would > * always align the requested size to page size > */ > - if (pool->gfp & GFP_ATOMIC) > + if ((pool->gfp & GFP_ATOMIC) == GFP_ATOMIC) > slot = kmalloc_node(size, pool->gfp, cpu_to_node(i)); > else > slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
diff --git a/lib/objpool.c b/lib/objpool.c index 234f9d0bd081..fd108fe0d095 100644 --- a/lib/objpool.c +++ b/lib/objpool.c @@ -76,7 +76,7 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs, * mimimal size of vmalloc is one page since vmalloc would * always align the requested size to page size */ - if (pool->gfp & GFP_ATOMIC) + if ((pool->gfp & GFP_ATOMIC) == GFP_ATOMIC) slot = kmalloc_node(size, pool->gfp, cpu_to_node(i)); else slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
objpool intends to use vmalloc for default (non-atomic) allocations of percpu slots and objects. However, the condition checking if GFP flags are equal to GFP_ATOMIC is wrong b/c GFP_ATOMIC is a combination of bits (__GFP_HIGH|__GFP_KSWAPD_RECLAIM) and so `pool->gfp & GFP_ATOMIC` will be true if either bit is set. Since GFP_ATOMIC and GFP_KERNEL share the ___GFP_KSWAPD_RECLAIM bit, kmalloc will be used in cases when GFP_KERNEL is specified, i.e. in all current usages of objpool. This may lead to unexpected OOM errors since kmalloc cannot allocate large amounts of memory. For instance, objpool is used by fprobe rethook which in turn is used by BPF kretprobe.multi and kprobe.session probe types. Trying to attach these to all kernel functions with libbpf using SEC("kprobe.session/*") int kprobe(struct pt_regs *ctx) { [...] } fails on objpool slot allocation with ENOMEM. Fix the condition to truly use vmalloc by default. Fixes: b4edb8d2d464 ("lib: objpool added: ring-array based lockless MPMC") Signed-off-by: Viktor Malik <vmalik@redhat.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Reviewed-by: Matt Wu <wuqiang.matt@bytedance.com> --- lib/objpool.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)