From nobody Sat Feb 7 17:42:11 2026 Received: from mail-ej1-f73.google.com (mail-ej1-f73.google.com [209.85.218.73]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3D9694207F for ; Fri, 22 Nov 2024 15:40:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.218.73 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732290062; cv=none; b=fTYAHnHyWQh9d1usP5TgBQQf0yCfBxy9MLOY9CWWqgS07eqa6+jwWQ2bl92FWppsVtAATLEDkbBAEyabqq6itCWhnoJZ3Xon6i6RvIFOEYH2r9HI2p7sYz2VdJHiWJzf5iKVLKgXPIKRI7PhoLZILppLqP4unMMQnta+EEfMmQw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732290062; c=relaxed/simple; bh=eY74rpC1y4FpYpbxCE7W6Ow6T3LIcTFrZGXMApjCveU=; h=Date:Mime-Version:Message-ID:Subject:From:To:Cc:Content-Type; b=Qh9hIJdsRBfZm5Fbg6SozB55OBhlFjKhb1fAdbkfQe/R1+BLIlm/A+ePZCXKGqx/AG2mIJO/UfN5joAisfyhMlcXf5yTybxmUuD1FFbc93NvGvL2AcHDwrZlAedXxccJgu5c/yvf791qNGgZWLYA47AhkaKjdg8/0Yuhq1L0H+A= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--elver.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=wrwb6H55; arc=none smtp.client-ip=209.85.218.73 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--elver.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="wrwb6H55" Received: by mail-ej1-f73.google.com with SMTP id a640c23a62f3a-a99fff1ad9cso160300866b.2 for ; Fri, 22 Nov 2024 07:40:59 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1732290058; x=1732894858; darn=vger.kernel.org; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=xTxOguFgwy9tOkyUrOPXOUVNTctOk0wNzBQXya5aVos=; b=wrwb6H55JK3J3G5/T8nPK1CnCA7VsupS8iNE74ilYlJ/SwOZFUh4XqHXrERFpd+x7v qcxUMZCt+B/iCv0HJJqNhfdMLkDUIWxb9tg5k/EM2gd0WcdflscEsmcPF168hhEegsHp iPTHQovm7Nde3eAc4fA666k+ubf4bEptDUM9hTsQMdMlrQnS0x4pfHAjuD3sMmrdTHqI BPo/KVTGMWbtL7WMk7LYEur7QQNHFGoKi/Z2QE5jID4L5E9LKesKCFBMjnuvn8r/yNEg MUh/UdbcY0R9F9v53zQ3KiF7AGByv5r1yg/01SRPsChWGMY2VRpR5VGwOt8KXYQk15Oh dAMw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1732290058; x=1732894858; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=xTxOguFgwy9tOkyUrOPXOUVNTctOk0wNzBQXya5aVos=; b=ixQCpZrt9wobj++mnMdEkAotjDhqguOBPq6yN+3AUkuYKtD9Nv5MinjxPvx5SV0nIw 9qdpDKiw9dfZc2lKdwfz2uf9ugQa5+65TgzIpRa1rFTlDsGW2wUYK6zyn/g18lrmA24v zu+2MhhHthGw0lyZKSPfOsdoyUiL6QBLPcKe8keue66jUPmlyDzzvgBvqphJa68LU1l0 JsDBi635ye6pa4Gr01B258TY8WESzeaEHVqMrlmAosZpwfeGUQFytX/5ZkeKWZQEOgim tD/+rSwhQ8CPF+w3674ZalTs1nK2zSaYydn/zXH63CU6Q2nT+9bgxAgs8fmrr3CNR5AP Upbw== X-Forwarded-Encrypted: i=1; AJvYcCX9Yjb33sOcB4O9uj93TbR4Zl4+bS88XTcz5fI6kcOSB+hYDSfqUiUgO2WyCMB4zBTgs/Ikz59lNCoVxlg=@vger.kernel.org X-Gm-Message-State: AOJu0YxVMOevq5yhVnc6QxSgZT0Ob/M8zB54X0KrT0SPU1fiwbhhJ+1W uOA9XkDHs5EVLEf2wu2dyjmdjxn0qltLLevAg5VJQUMl4TQzo+rTMXDV2D4j3XZdabf8Gplu9g= = X-Google-Smtp-Source: AGHT+IHC6kfIvPj3vG1i+LAY/CGzJaSxv8wDpDJqxPFx2Qz/GZuoQ+cNZBfybl6y2Mvx/LGv/9WCbm1jIg== X-Received: from elver.muc.corp.google.com ([2a00:79e0:9c:201:e369:a6f7:a3ea:97bb]) (user=elver job=sendgmr) by 2002:a17:906:f194:b0:a9a:11e5:c8d3 with SMTP id a640c23a62f3a-aa509bc55eamr69466b.6.1732290058216; Fri, 22 Nov 2024 07:40:58 -0800 (PST) Date: Fri, 22 Nov 2024 16:39:47 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 X-Mailer: git-send-email 2.47.0.371.ga323438b13-goog Message-ID: <20241122154051.3914732-1-elver@google.com> Subject: [PATCH] stackdepot: fix stack_depot_save_flags() in NMI context From: Marco Elver To: elver@google.com, Andrew Morton Cc: Andrey Konovalov , Alexander Potapenko , Dmitry Vyukov , Vlastimil Babka , Oscar Salvador , linux-kernel@vger.kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, Sebastian Andrzej Siewior Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Per documentation, stack_depot_save_flags() was meant to be usable from NMI context if STACK_DEPOT_FLAG_CAN_ALLOC is unset. However, it still would try to take the pool_lock in an attempt to save a stack trace in the current pool (if space is available). This could result in deadlock if an NMI is handled while pool_lock is already held. To avoid deadlock, only try to take the lock in NMI context and give up if unsuccessful. The documentation is fixed to clearly convey this. Link: https://lkml.kernel.org/r/Z0CcyfbPqmxJ9uJH@elver.google.com Fixes: 4434a56ec209 ("stackdepot: make fast paths lock-less again") Reported-by: Sebastian Andrzej Siewior Signed-off-by: Marco Elver Reviewed-by: Sebastian Andrzej Siewior --- include/linux/stackdepot.h | 6 +++--- lib/stackdepot.c | 10 +++++++++- 2 files changed, 12 insertions(+), 4 deletions(-) diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h index e9ec32fb97d4..2cc21ffcdaf9 100644 --- a/include/linux/stackdepot.h +++ b/include/linux/stackdepot.h @@ -147,7 +147,7 @@ static inline int stack_depot_early_init(void) { return= 0; } * If the provided stack trace comes from the interrupt context, only the = part * up to the interrupt entry is saved. * - * Context: Any context, but setting STACK_DEPOT_FLAG_CAN_ALLOC is require= d if + * Context: Any context, but unsetting STACK_DEPOT_FLAG_CAN_ALLOC is requi= red if * alloc_pages() cannot be used from the current context. Current= ly * this is the case for contexts where neither %GFP_ATOMIC nor * %GFP_NOWAIT can be used (NMI, raw_spin_lock). @@ -156,7 +156,7 @@ static inline int stack_depot_early_init(void) { return= 0; } */ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries, unsigned int nr_entries, - gfp_t gfp_flags, + gfp_t alloc_flags, depot_flags_t depot_flags); =20 /** @@ -175,7 +175,7 @@ depot_stack_handle_t stack_depot_save_flags(unsigned lo= ng *entries, * Return: Handle of the stack trace stored in depot, 0 on failure */ depot_stack_handle_t stack_depot_save(unsigned long *entries, - unsigned int nr_entries, gfp_t gfp_flags); + unsigned int nr_entries, gfp_t alloc_flags); =20 /** * __stack_depot_get_stack_record - Get a pointer to a stack_record struct diff --git a/lib/stackdepot.c b/lib/stackdepot.c index 5ed34cc963fc..245d5b416699 100644 --- a/lib/stackdepot.c +++ b/lib/stackdepot.c @@ -630,7 +630,15 @@ depot_stack_handle_t stack_depot_save_flags(unsigned l= ong *entries, prealloc =3D page_address(page); } =20 - raw_spin_lock_irqsave(&pool_lock, flags); + if (in_nmi()) { + /* We can never allocate in NMI context. */ + WARN_ON_ONCE(can_alloc); + /* Best effort; bail if we fail to take the lock. */ + if (!raw_spin_trylock_irqsave(&pool_lock, flags)) + goto exit; + } else { + raw_spin_lock_irqsave(&pool_lock, flags); + } printk_deferred_enter(); =20 /* Try to find again, to avoid concurrently inserting duplicates. */ --=20 2.47.0.371.ga323438b13-goog