From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-181.mta0.migadu.com (out-181.mta0.migadu.com [91.218.175.181]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 98A79219E98 for ; Fri, 24 Jan 2025 20:21:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.181 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737750073; cv=none; b=cwAJUS7Xvl8YhXymArsUaB3cLQznaYa4C9Wtypq2tk4cmiCABNehWGeIkhY2+Ftp3VChTIwuZ1CJfjNpYxRxRXH2xoAlyEso5FDc+coy5h50ooJyORhZEfWqOaOj7xURfXnLUYmq37AxGNoxHtGlxhvoh7n26xqrlSGGNjLm9zU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737750073; c=relaxed/simple; bh=Yb1W1gjJqHwl1D4aMg6xgGWVL9WrsI7znMGCeIRMM5E=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=tPl+RtiX89EFUs+wnXPerWjPZWPTp+IjgeRywvcP7ss2KQYSHsjC7MPPIB9l2tqSPYnq37Hy+dm5Lcag62QSbQxv2H6S1jATXH7bQ5xZbvAACqzWLOLlI6hHrx29mjfnOWE0b4bIo46c18tDEgkOWaJXGFLj4F6wvoy73U/sISU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=DtvJlfcJ; arc=none smtp.client-ip=91.218.175.181 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="DtvJlfcJ" Message-ID: <02c69185-1477-485c-af4f-a46f7aadadab@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1737750054; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=YB9Lkx2YLsx81q0woXn4RYBLPtp8YNlgiS03lX4O1zc=; b=DtvJlfcJfZ3EE/MgqSFwKX/dT7w/cfgHzpTaA5Yi37ktQFVhaleZdSp2/U9pLQMnmXvWge 1OUpENRtzOO1ZRT2Ub1EWyx/3VR5btmtPmfgiNMTlDyLTND2m42bdvdFgOAf9HbsZadcwu 3Ux8q3DI3kiWk7l7UfIKgRyuWx+uKvE= Date: Fri, 24 Jan 2025 12:20:48 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf v2] bpf: Fix deadlock when freeing cgroup storage To: Abel Wu Cc: Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , David Vernet , "open list:BPF [STORAGE & CGROUPS]" , open list References: <20241221061018.37717-1-wuyun.abel@bytedance.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau Content-Language: en-US In-Reply-To: <20241221061018.37717-1-wuyun.abel@bytedance.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 12/20/24 10:10 PM, Abel Wu wrote: > The following commit > bc235cdb423a ("bpf: Prevent deadlock from recursive bpf_task_storage_[get|delete]") > first introduced deadlock prevention for fentry/fexit programs attaching > on bpf_task_storage helpers. That commit also employed the logic in map > free path in its v6 version. > > Later bpf_cgrp_storage was first introduced in > c4bcfb38a95e ("bpf: Implement cgroup storage available to non-cgroup-attached bpf progs") > which faces the same issue as bpf_task_storage, instead of its busy > counter, NULL was passed to bpf_local_storage_map_free() which opened > a window to cause deadlock: > > > (acquiring local_storage->lock) > _raw_spin_lock_irqsave+0x3d/0x50 > bpf_local_storage_update+0xd1/0x460 > bpf_cgrp_storage_get+0x109/0x130 > bpf_prog_a4d4a370ba857314_cgrp_ptr+0x139/0x170 > ? __bpf_prog_enter_recur+0x16/0x80 > bpf_trampoline_6442485186+0x43/0xa4 > cgroup_storage_ptr+0x9/0x20 > (holding local_storage->lock) > bpf_selem_unlink_storage_nolock.constprop.0+0x135/0x160 > bpf_selem_unlink_storage+0x6f/0x110 > bpf_local_storage_map_free+0xa2/0x110 > bpf_map_free_deferred+0x5b/0x90 > process_one_work+0x17c/0x390 > worker_thread+0x251/0x360 > kthread+0xd2/0x100 > ret_from_fork+0x34/0x50 > ret_from_fork_asm+0x1a/0x30 > > > Progs: > - A: SEC("fentry/cgroup_storage_ptr") The v1 thread has suggested using notrace in a few functions. I didn't see any counterarguments that wouldn't be sufficient. imo, that should be a better option instead of having more unnecessary failures in all other normal use cases which will not be interested in tracing cgroup_storage_ptr(). pw-bot: cr > - cgid (BPF_MAP_TYPE_HASH) > Record the id of the cgroup the current task belonging > to in this hash map, using the address of the cgroup > as the map key. > - cgrpa (BPF_MAP_TYPE_CGRP_STORAGE) > If current task is a kworker, lookup the above hash > map using function parameter @owner as the key to get > its corresponding cgroup id which is then used to get > a trusted pointer to the cgroup through > bpf_cgroup_from_id(). This trusted pointer can then > be passed to bpf_cgrp_storage_get() to finally trigger > the deadlock issue. > - B: SEC("tp_btf/sys_enter") > - cgrpb (BPF_MAP_TYPE_CGRP_STORAGE) > The only purpose of this prog is to fill Prog A's > hash map by calling bpf_cgrp_storage_get() for as > many userspace tasks as possible. > > Steps to reproduce: > - Run A; > - while (true) { Run B; Destroy B; } > > Fix this issue by passing its busy counter to the free procedure so > it can be properly incremented before storage/smap locking. > > Fixes: c4bcfb38a95e ("bpf: Implement cgroup storage available to non-cgroup-attached bpf progs") > Signed-off-by: Abel Wu > --- > kernel/bpf/bpf_cgrp_storage.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/bpf/bpf_cgrp_storage.c b/kernel/bpf/bpf_cgrp_storage.c > index 20f05de92e9c..7996fcea3755 100644 > --- a/kernel/bpf/bpf_cgrp_storage.c > +++ b/kernel/bpf/bpf_cgrp_storage.c > @@ -154,7 +154,7 @@ static struct bpf_map *cgroup_storage_map_alloc(union bpf_attr *attr) > > static void cgroup_storage_map_free(struct bpf_map *map) > { > - bpf_local_storage_map_free(map, &cgroup_cache, NULL); > + bpf_local_storage_map_free(map, &cgroup_cache, &bpf_cgrp_storage_busy); > } > > /* *gfp_flags* is a hidden argument provided by the verifier */