From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 B8E7B16C434; Thu, 18 Apr 2024 15:46:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713455217; cv=none; b=c05KP7fv9k7kns9zlePbUCKnmw4da2cZAjFFoNBkQpvic2JJPb1FJzXW48HPJh7BXjfveHETqEiKgbkfNAtjsdD1mMVNi4WRk4sOteBj7XkIu5I0aL9BTiHeNMXWbyCwD2MhN75gORSsC0vGARJHqOZwXxqhHIrCpSFDiq0woB4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1713455217; c=relaxed/simple; bh=CSADx2CB69mfT8jOoCkrOeYysFybh9E9rmHaG61n528=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Zl8cF2dqe22SkJlno8aFU4TFmDmhYsAmETPJjRv6h8F2N95YiCWefbBMeQsi2SqH+iD0FECmIYOtq48bGLoPg/rkXWrf9rwHbwW1uob9pfOwUsLnGx3y4GCe5OD63isAfl5OMBRo2atjZUnAke56bZtMXyIcjiHtBX2OZdvbvmc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vFKzHdH8; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vFKzHdH8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 42706C32782; Thu, 18 Apr 2024 15:46:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1713455217; bh=CSADx2CB69mfT8jOoCkrOeYysFybh9E9rmHaG61n528=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=vFKzHdH8ja1Efdd5hQT3JgGoW263bR7EeNpDUDXUL4XVWanxMqJFbAsotyQVmMfl/ ePCIcAsmDs8qRilsFGd3NH7z4uA263dKdJa1HXenInrxspe2ju92SHDkXDwGUiuPp7 mvyw0N/G6GNCzhKvmDSAiIK8UtpzE3b//hVFixWbPZCaG0gO447yNkPo8L6QzmYyLo wNUqTpIy9A68SZK0SFhPhbeFUeRZyLU1CCng/vvbuU+78cB2zD3gEonJSz1fyEDCMg kr4QKlgpO+KuvLmggUB8IjAozvMJdEhktlyYkotv29xJdb/oFvcTldMS4aoIFazC+2 BVX6Un8RfU9TA== Date: Thu, 18 Apr 2024 17:46:55 +0200 From: Frederic Weisbecker To: Haifeng Xu , mingo@kernel.org Cc: peterz@infradead.org, mingo@redhat.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3] perf/core: Fix missing wakeup when waiting for context reference Message-ID: References: <20240418114209.22233-1-haifeng.xu@shopee.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240418114209.22233-1-haifeng.xu@shopee.com> Le Thu, Apr 18, 2024 at 11:42:09AM +0000, Haifeng Xu a écrit : > In our production environment, we found many hung tasks which are > blocked for more than 18 hours. Their call traces are like this: > > [346278.191038] __schedule+0x2d8/0x890 > [346278.191046] schedule+0x4e/0xb0 > [346278.191049] perf_event_free_task+0x220/0x270 > [346278.191056] ? init_wait_var_entry+0x50/0x50 > [346278.191060] copy_process+0x663/0x18d0 > [346278.191068] kernel_clone+0x9d/0x3d0 > [346278.191072] __do_sys_clone+0x5d/0x80 > [346278.191076] __x64_sys_clone+0x25/0x30 > [346278.191079] do_syscall_64+0x5c/0xc0 > [346278.191083] ? syscall_exit_to_user_mode+0x27/0x50 > [346278.191086] ? do_syscall_64+0x69/0xc0 > [346278.191088] ? irqentry_exit_to_user_mode+0x9/0x20 > [346278.191092] ? irqentry_exit+0x19/0x30 > [346278.191095] ? exc_page_fault+0x89/0x160 > [346278.191097] ? asm_exc_page_fault+0x8/0x30 > [346278.191102] entry_SYSCALL_64_after_hwframe+0x44/0xae > > The task was waiting for the refcount become to 1, but from the vmcore, > we found the refcount has already been 1. It seems that the task didn't > get woken up by perf_event_release_kernel() and got stuck forever. The > below scenario may cause the problem. > > Thread A Thread B > ... ... > perf_event_free_task perf_event_release_kernel > ... > acquire event->child_mutex > ... > get_ctx > ... release event->child_mutex > acquire ctx->mutex > ... > perf_free_event (acquire/release event->child_mutex) > ... > release ctx->mutex > wait_var_event > acquire ctx->mutex > acquire event->child_mutex > # move existing events to free_list > release event->child_mutex > release ctx->mutex > put_ctx > ... ... > > In this case, all events of the ctx have been freed, so we couldn't > find the ctx in free_list and Thread A will miss the wakeup. It's thus > necessary to add a wakeup after dropping the reference. > > Fixes: 1cf8dfe8a661 ("perf/core: Fix race between close() and fork()") > Signed-off-by: Haifeng Xu > Reviewed-by: Frederic Weisbecker Thanks!