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 7DE402E2DF4; Wed, 28 Jan 2026 15:55:18 +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=1769615718; cv=none; b=nDzi2c+7g4geH/jc0yzGNZEzZTPuwI9JU9iAngOPcFS1zJk83CogMsmiob//mliJjDvv2cSEFVJzWRKtEHuXgJPLQvURsvSGGjm+1XEn029iL/EFwdDXxvcSCpM4WYE0D5hF5YgmaoXBxpo00EWQIEPt1Pv07EBWdWG2HkLqZK0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769615718; c=relaxed/simple; bh=BgP9RYOwphCiCixSjUyFgl+dL1D4iOEJmrOR77KfV4A=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Wktm0vqNLSUj8WPMrCAks6kw2kgwDE3eKMHRH9MR7KuNpaGOf5rcCasdQbGhIgzoNlHlhkbf6eKg7wa3VUIHBz9Q+wW4ttZRkWEsv3cMLXpZ+VoVYB3X4kzTAys0RKivtZhZgEfZX6/cHgpX3iEDCzQYoy6LxBPs9wVc5ZSjktA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=XuQH+hMJ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="XuQH+hMJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E0ADEC4CEF1; Wed, 28 Jan 2026 15:55:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1769615718; bh=BgP9RYOwphCiCixSjUyFgl+dL1D4iOEJmrOR77KfV4A=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XuQH+hMJCA6ZBm6R/xvJHrjA/+w4lbM1T2akAmcK6NBd6LFhws/jFRtrcOevybMY6 T3nnGWgDLYP7i0kxJVRfkyGPwMWYvYcl55g+nojvH40d4ACwM5Da8Z9zS99NVMqb4J AetTI4XxxvD98ziaJFOHEaLyI95VvvJLXvzvLqMM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, David Jeffery , Bart Van Assche , "Martin K. Petersen" , Sasha Levin Subject: [PATCH 6.18 092/227] scsi: core: Wake up the error handler when final completions race against each other Date: Wed, 28 Jan 2026 16:22:17 +0100 Message-ID: <20260128145347.645150435@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260128145344.331957407@linuxfoundation.org> References: <20260128145344.331957407@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: David Jeffery [ Upstream commit fe2f8ad6f0999db3b318359a01ee0108c703a8c3 ] The fragile ordering between marking commands completed or failed so that the error handler only wakes when the last running command completes or times out has race conditions. These race conditions can cause the SCSI layer to fail to wake the error handler, leaving I/O through the SCSI host stuck as the error state cannot advance. First, there is an memory ordering issue within scsi_dec_host_busy(). The write which clears SCMD_STATE_INFLIGHT may be reordered with reads counting in scsi_host_busy(). While the local CPU will see its own write, reordering can allow other CPUs in scsi_dec_host_busy() or scsi_eh_inc_host_failed() to see a raised busy count, causing no CPU to see a host busy equal to the host_failed count. This race condition can be prevented with a memory barrier on the error path to force the write to be visible before counting host busy commands. Second, there is a general ordering issue with scsi_eh_inc_host_failed(). By counting busy commands before incrementing host_failed, it can race with a final command in scsi_dec_host_busy(), such that scsi_dec_host_busy() does not see host_failed incremented but scsi_eh_inc_host_failed() counts busy commands before SCMD_STATE_INFLIGHT is cleared by scsi_dec_host_busy(), resulting in neither waking the error handler task. This needs the call to scsi_host_busy() to be moved after host_failed is incremented to close the race condition. Fixes: 6eb045e092ef ("scsi: core: avoid host-wide host_busy counter for scsi_mq") Signed-off-by: David Jeffery Reviewed-by: Bart Van Assche Link: https://patch.msgid.link/20260113161036.6730-1-djeffery@redhat.com Signed-off-by: Martin K. Petersen Signed-off-by: Sasha Levin --- drivers/scsi/scsi_error.c | 11 ++++++++++- drivers/scsi/scsi_lib.c | 8 ++++++++ 2 files changed, 18 insertions(+), 1 deletion(-) diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c index 830429483319a..2fd4ca96b3089 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -282,11 +282,20 @@ static void scsi_eh_inc_host_failed(struct rcu_head *head) { struct scsi_cmnd *scmd = container_of(head, typeof(*scmd), rcu); struct Scsi_Host *shost = scmd->device->host; - unsigned int busy = scsi_host_busy(shost); + unsigned int busy; unsigned long flags; spin_lock_irqsave(shost->host_lock, flags); shost->host_failed++; + spin_unlock_irqrestore(shost->host_lock, flags); + /* + * The counting of busy requests needs to occur after adding to + * host_failed or after the lock acquire for adding to host_failed + * to prevent a race with host unbusy and missing an eh wakeup. + */ + busy = scsi_host_busy(shost); + + spin_lock_irqsave(shost->host_lock, flags); scsi_eh_wakeup(shost, busy); spin_unlock_irqrestore(shost->host_lock, flags); } diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index d7e42293b8645..7ddb73cd6d9fe 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -376,6 +376,14 @@ static void scsi_dec_host_busy(struct Scsi_Host *shost, struct scsi_cmnd *cmd) rcu_read_lock(); __clear_bit(SCMD_STATE_INFLIGHT, &cmd->state); if (unlikely(scsi_host_in_recovery(shost))) { + /* + * Ensure the clear of SCMD_STATE_INFLIGHT is visible to + * other CPUs before counting busy requests. Otherwise, + * reordering can cause CPUs to race and miss an eh wakeup + * when no CPU sees all busy requests as done or timed out. + */ + smp_mb(); + unsigned int busy = scsi_host_busy(shost); spin_lock_irqsave(shost->host_lock, flags); -- 2.51.0