From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96F7FC38A2A for ; Fri, 8 May 2020 13:48:33 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 08EF520A8B for ; Fri, 8 May 2020 13:48:32 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=ellerman.id.au header.i=@ellerman.id.au header.b="Jzbub23r" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 08EF520A8B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 49JWrD5r7CzDr7G for ; Fri, 8 May 2020 23:48:28 +1000 (AEST) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 49JVvj1bGPzDr5d for ; Fri, 8 May 2020 23:06:25 +1000 (AEST) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=Jzbub23r; dkim-atps=neutral Received: by ozlabs.org (Postfix) id 49JVvb5YQBz9sWh; Fri, 8 May 2020 23:06:19 +1000 (AEST) Received: by ozlabs.org (Postfix, from userid 1034) id 49JVvZ6wKrz9sWj; Fri, 8 May 2020 23:06:18 +1000 (AEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1588943179; bh=1GN005tbj9IwratrslGZWMhNVJ3NhNCQjUVhN8c5D2U=; h=From:To:Cc:Subject:Date:From; b=Jzbub23rJVn/BR3RdqugN8DQ9yT8mG7a1+0w19N6mxUfTFMZy8CtKzwkJQlXFaRsZ 2pnvbDNxE0A5thvOXob6da3laRC2f8d2NRN/kodeF+m1Z0obFS51LCzEM50b0B0MPs Ifq/05bjExuUEZWp+f6A6IAapui+v42lJNT9wqzsTMM5UWT3puz+kJBDSXgVs2tn5x lHwp5k3EJ97puWxtXfBUUaTii1PW8jD6vbQRaKUpAoYsDVA2Bwsb5h6BDRfBcd7SrU 1iZud8dVlik0Qlz2EPQCO3q4myLZYNab3U+38vLQbmsSFXjL2uD1YvYXIpgjc3GwT8 XH/kA8+EwXHwA== From: Michael Ellerman To: linuxppc-dev@ozlabs.org Subject: [PATCH v2] powerpc/spufs: Rework fcheck() usage Date: Fri, 8 May 2020 23:06:33 +1000 Message-Id: <20200508130633.2532759-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: hch@lst.de, jk@ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Currently the spu coredump code triggers an RCU warning: ============================= WARNING: suspicious RCU usage 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Not tainted ----------------------------- include/linux/fdtable.h:95 suspicious rcu_dereference_check() usage! other info that might help us debug this: rcu_scheduler_active = 2, debug_locks = 1 1 lock held by spu-coredump/1343: #0: c0000007fa22f430 (sb_writers#2){.+.+}-{0:0}, at: .do_coredump+0x1010/0x13c8 stack backtrace: CPU: 0 PID: 1343 Comm: spu-coredump Not tainted 5.7.0-rc3-01755-g7cd49f0b7ec7 #1 Call Trace: .dump_stack+0xec/0x15c (unreliable) .lockdep_rcu_suspicious+0x120/0x144 .coredump_next_context+0x148/0x158 .spufs_coredump_extra_notes_size+0x54/0x190 .elf_coredump_extra_notes_size+0x34/0x50 .elf_core_dump+0xe48/0x19d0 .do_coredump+0xe50/0x13c8 .get_signal+0x864/0xd88 .do_notify_resume+0x158/0x3c8 .interrupt_exit_user_prepare+0x19c/0x208 interrupt_return+0x14/0x1c0 This comes from fcheck_files() via fcheck(). It's pretty clearly documented that fcheck() must be wrapped with rcu_read_lock(), adding that fixes the RCU warning. hch points out that once we've released the RCU read lock the file may be closed and freed, which would leave us with a pointer to a freed spu_context. To avoid that, take a reference to the spu_context while we hold the RCU read lock, and drop that reference later once we're done with the context. Signed-off-by: Michael Ellerman --- arch/powerpc/platforms/cell/spufs/coredump.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) v2: Take a reference and hold it until we're done. diff --git a/arch/powerpc/platforms/cell/spufs/coredump.c b/arch/powerpc/platforms/cell/spufs/coredump.c index 8b3296b62f65..37c155254cd5 100644 --- a/arch/powerpc/platforms/cell/spufs/coredump.c +++ b/arch/powerpc/platforms/cell/spufs/coredump.c @@ -82,13 +82,20 @@ static int match_context(const void *v, struct file *file, unsigned fd) */ static struct spu_context *coredump_next_context(int *fd) { + struct spu_context *ctx; struct file *file; int n = iterate_fd(current->files, *fd, match_context, NULL); if (!n) return NULL; *fd = n - 1; + + rcu_read_lock(); file = fcheck(*fd); - return SPUFS_I(file_inode(file))->i_ctx; + ctx = SPUFS_I(file_inode(file))->i_ctx; + get_spu_context(ctx); + rcu_read_unlock(); + + return ctx; } int spufs_coredump_extra_notes_size(void) @@ -99,17 +106,23 @@ int spufs_coredump_extra_notes_size(void) fd = 0; while ((ctx = coredump_next_context(&fd)) != NULL) { rc = spu_acquire_saved(ctx); - if (rc) + if (rc) { + put_spu_context(ctx); break; + } + rc = spufs_ctx_note_size(ctx, fd); spu_release_saved(ctx); - if (rc < 0) + if (rc < 0) { + put_spu_context(ctx); break; + } size += rc; /* start searching the next fd next time */ fd++; + put_spu_context(ctx); } return size; -- 2.25.1