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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0D3F5C433FE for ; Tue, 5 Apr 2022 12:31:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1383128AbiDEMY4 (ORCPT ); Tue, 5 Apr 2022 08:24:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58046 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355857AbiDEKWK (ORCPT ); Tue, 5 Apr 2022 06:22:10 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 411A7A5EAD; Tue, 5 Apr 2022 03:05:13 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 2F3C16167E; Tue, 5 Apr 2022 10:05:13 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 32416C385A1; Tue, 5 Apr 2022 10:05:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649153112; bh=ZcVQpwvFrXJtLOsqi3jPXEcTtdIZsDWqBIA96z9gCqY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ePSBlrTNElE/oHLICPC9XdCdNoLK9p1Eqqasiy+Pdb+6KH9vb//bmeV1785Q7G6CM NaMm5Es2xtQM9AC+OqSd/N0293aFVyOxtap0hULlSX+W6Xzc5FFLkepO3aVmTwT30n y8HjL49zx4NR9xiBJ702r2cfl5+TLsOM6ACWBtfM= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Sebastian Andrzej Siewior , Jann Horn , Kees Cook Subject: [PATCH 5.10 105/599] pstore: Dont use semaphores in always-atomic-context code Date: Tue, 5 Apr 2022 09:26:39 +0200 Message-Id: <20220405070301.958868258@linuxfoundation.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220405070258.802373272@linuxfoundation.org> References: <20220405070258.802373272@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Jann Horn commit 8126b1c73108bc691f5643df19071a59a69d0bc6 upstream. pstore_dump() is *always* invoked in atomic context (nowadays in an RCU read-side critical section, before that under a spinlock). It doesn't make sense to try to use semaphores here. This is mostly a revert of commit ea84b580b955 ("pstore: Convert buf_lock to semaphore"), except that two parts aren't restored back exactly as they were: - keep the lock initialization in pstore_register - in efi_pstore_write(), always set the "block" flag to false - omit "is_locked", that was unnecessary since commit 959217c84c27 ("pstore: Actually give up during locking failure") - fix the bailout message The actual problem that the buggy commit was trying to address may have been that the use of preemptible() in efi_pstore_write() was wrong - it only looks at preempt_count() and the state of IRQs, but __rcu_read_lock() doesn't touch either of those under CONFIG_PREEMPT_RCU. (Sidenote: CONFIG_PREEMPT_RCU means that the scheduler can preempt tasks in RCU read-side critical sections, but you're not allowed to actively block/reschedule.) Lockdep probably never caught the problem because it's very rare that you actually hit the contended case, so lockdep always just sees the down_trylock(), not the down_interruptible(), and so it can't tell that there's a problem. Fixes: ea84b580b955 ("pstore: Convert buf_lock to semaphore") Cc: stable@vger.kernel.org Acked-by: Sebastian Andrzej Siewior Signed-off-by: Jann Horn Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20220314185953.2068993-1-jannh@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/firmware/efi/efi-pstore.c | 2 +- fs/pstore/platform.c | 38 ++++++++++++++++++-------------------- include/linux/pstore.h | 6 +++--- 3 files changed, 22 insertions(+), 24 deletions(-) --- a/drivers/firmware/efi/efi-pstore.c +++ b/drivers/firmware/efi/efi-pstore.c @@ -266,7 +266,7 @@ static int efi_pstore_write(struct pstor efi_name[i] = name[i]; ret = efivar_entry_set_safe(efi_name, vendor, PSTORE_EFI_ATTRIBUTES, - preemptible(), record->size, record->psi->buf); + false, record->size, record->psi->buf); if (record->reason == KMSG_DUMP_OOPS && try_module_get(THIS_MODULE)) if (!schedule_work(&efivar_work)) --- a/fs/pstore/platform.c +++ b/fs/pstore/platform.c @@ -143,21 +143,22 @@ static void pstore_timer_kick(void) mod_timer(&pstore_timer, jiffies + msecs_to_jiffies(pstore_update_ms)); } -/* - * Should pstore_dump() wait for a concurrent pstore_dump()? If - * not, the current pstore_dump() will report a failure to dump - * and return. - */ -static bool pstore_cannot_wait(enum kmsg_dump_reason reason) +static bool pstore_cannot_block_path(enum kmsg_dump_reason reason) { - /* In NMI path, pstore shouldn't block regardless of reason. */ + /* + * In case of NMI path, pstore shouldn't be blocked + * regardless of reason. + */ if (in_nmi()) return true; switch (reason) { /* In panic case, other cpus are stopped by smp_send_stop(). */ case KMSG_DUMP_PANIC: - /* Emergency restart shouldn't be blocked. */ + /* + * Emergency restart shouldn't be blocked by spinning on + * pstore_info::buf_lock. + */ case KMSG_DUMP_EMERG: return true; default: @@ -388,21 +389,19 @@ static void pstore_dump(struct kmsg_dump unsigned long total = 0; const char *why; unsigned int part = 1; + unsigned long flags = 0; int ret; why = kmsg_dump_reason_str(reason); - if (down_trylock(&psinfo->buf_lock)) { - /* Failed to acquire lock: give up if we cannot wait. */ - if (pstore_cannot_wait(reason)) { - pr_err("dump skipped in %s path: may corrupt error record\n", - in_nmi() ? "NMI" : why); - return; - } - if (down_interruptible(&psinfo->buf_lock)) { - pr_err("could not grab semaphore?!\n"); + if (pstore_cannot_block_path(reason)) { + if (!spin_trylock_irqsave(&psinfo->buf_lock, flags)) { + pr_err("dump skipped in %s path because of concurrent dump\n", + in_nmi() ? "NMI" : why); return; } + } else { + spin_lock_irqsave(&psinfo->buf_lock, flags); } oopscount++; @@ -464,8 +463,7 @@ static void pstore_dump(struct kmsg_dump total += record.size; part++; } - - up(&psinfo->buf_lock); + spin_unlock_irqrestore(&psinfo->buf_lock, flags); } static struct kmsg_dumper pstore_dumper = { @@ -591,7 +589,7 @@ int pstore_register(struct pstore_info * psi->write_user = pstore_write_user_compat; psinfo = psi; mutex_init(&psinfo->read_mutex); - sema_init(&psinfo->buf_lock, 1); + spin_lock_init(&psinfo->buf_lock); if (psi->flags & PSTORE_FLAGS_DMESG) allocate_buf_for_compression(); --- a/include/linux/pstore.h +++ b/include/linux/pstore.h @@ -14,7 +14,7 @@ #include #include #include -#include +#include #include #include @@ -87,7 +87,7 @@ struct pstore_record { * @owner: module which is responsible for this backend driver * @name: name of the backend driver * - * @buf_lock: semaphore to serialize access to @buf + * @buf_lock: spinlock to serialize access to @buf * @buf: preallocated crash dump buffer * @bufsize: size of @buf available for crash dump bytes (must match * smallest number of bytes available for writing to a @@ -178,7 +178,7 @@ struct pstore_info { struct module *owner; const char *name; - struct semaphore buf_lock; + spinlock_t buf_lock; char *buf; size_t bufsize;