From patchwork Fri Jan 31 23:16:31 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Morton X-Patchwork-Id: 232288 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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED autolearn=no 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 C8B06C33CB7 for ; Fri, 31 Jan 2020 23:16:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8B1FC20CC7 for ; Fri, 31 Jan 2020 23:16:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580512593; bh=XEzTmYrDYJn92eZlCIN6APhWrl7NQ8UrZ9yTb1CN0do=; h=Date:From:To:Subject:List-ID:From; b=raJXcVws2RMd51ldUUQKW3VAB1mIOEkm9sosKvFOhgXMVEB6B0KNCEOM1FWEe/l28 FG0ZtVfWA+faLkrA/b3kkdVF4Qb5vt+/S2ObRjbLwJ8w5UGgto8LRICiGzZa9/7LAJ 4bbR49nHUr/3SjMP8q+IVzMNzkkIaFDIx7jeU0iQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726484AbgAaXQd (ORCPT ); Fri, 31 Jan 2020 18:16:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:48588 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726319AbgAaXQd (ORCPT ); Fri, 31 Jan 2020 18:16:33 -0500 Received: from localhost.localdomain (c-71-198-47-131.hsd1.ca.comcast.net [71.198.47.131]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9D9402071A; Fri, 31 Jan 2020 23:16:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580512591; bh=XEzTmYrDYJn92eZlCIN6APhWrl7NQ8UrZ9yTb1CN0do=; h=Date:From:To:Subject:From; b=tZZXnivh4OeYZAVJxSJqcnhNNA3BzWsdvfK09HDFYV2Kp2gFL97+JDRJlUGRDL04p ECRjsF8iAg8ExXlu+iLGauXRAi6i6G/x+xN1wsM+tv4D1oWrQx4pcjuVd3KjOnHa2e 5j1WR0AqR9AQKhX/3pl/LRjp73FSSc6wBDLhYW10= Date: Fri, 31 Jan 2020 15:16:31 -0800 From: akpm@linux-foundation.org To: axboe@kernel.dk, clm@fb.com, mm-commits@vger.kernel.org, stable@vger.kernel.org, tj@kernel.org, tytso@mit.edu Subject: [merged] memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears.patch removed from -mm tree Message-ID: <20200131231631.u9oGVG0n4%akpm@linux-foundation.org> User-Agent: s-nail v14.8.16 Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch titled Subject: memcg: fix a crash in wb_workfn when a device disappears has been removed from the -mm tree. Its filename was memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: "Theodore Ts'o" Subject: memcg: fix a crash in wb_workfn when a device disappears Without memcg, there is a one-to-one mapping between the bdi and bdi_writeback structures. In this world, things are fairly straightforward; the first thing bdi_unregister() does is to shutdown the bdi_writeback structure (or wb), and part of that writeback ensures that no other work queued against the wb, and that the wb is fully drained. With memcg, however, there is a one-to-many relationship between the bdi and bdi_writeback structures; that is, there are multiple wb objects which can all point to a single bdi. There is a refcount which prevents the bdi object from being released (and hence, unregistered). So in theory, the bdi_unregister() *should* only get called once its refcount goes to zero (bdi_put will drop the refcount, and when it is zero, release_bdi gets called, which calls bdi_unregister). Unfortunately, del_gendisk() in block/gen_hd.c never got the memo about the Brave New memcg World, and calls bdi_unregister directly. It does this without informing the file system, or the memcg code, or anything else. This causes the root wb associated with the bdi to be unregistered, but none of the memcg-specific wb's are shutdown. So when one of these wb's are woken up to do delayed work, they try to dereference their wb->bdi->dev to fetch the device name, but unfortunately bdi->dev is now NULL, thanks to the bdi_unregister() called by del_gendisk(). As a result, *boom*. Fortunately, it looks like the rest of the writeback path is perfectly happy with bdi->dev and bdi->owner being NULL, so the simplest fix is to create a bdi_dev_name() function which can handle bdi->dev being NULL. This also allows us to bulletproof the writeback tracepoints to prevent them from dereferencing a NULL pointer and crashing the kernel if one is tracing with memcg's enabled, and an iSCSI device dies or a USB storage stick is pulled. The most common way of triggering this will be hotremoval of a device while writeback with memcg enabled is going on. It was triggering several times a day in a heavily loaded production environment. Google Bug Id: 145475544 Link: https://lore.kernel.org/r/20191227194829.150110-1-tytso@mit.edu Link: http://lkml.kernel.org/r/20191228005211.163952-1-tytso@mit.edu Signed-off-by: Theodore Ts'o Cc: Chris Mason Cc: Tejun Heo Cc: Jens Axboe Cc: Signed-off-by: Andrew Morton --- fs/fs-writeback.c | 2 - include/linux/backing-dev.h | 10 +++++++ include/trace/events/writeback.h | 37 +++++++++++++---------------- mm/backing-dev.c | 1 4 files changed, 29 insertions(+), 21 deletions(-) --- a/fs/fs-writeback.c~memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears +++ a/fs/fs-writeback.c @@ -2063,7 +2063,7 @@ void wb_workfn(struct work_struct *work) struct bdi_writeback, dwork); long pages_written; - set_worker_desc("flush-%s", dev_name(wb->bdi->dev)); + set_worker_desc("flush-%s", bdi_dev_name(wb->bdi)); current->flags |= PF_SWAPWRITE; if (likely(!current_is_workqueue_rescuer() || --- a/include/linux/backing-dev.h~memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears +++ a/include/linux/backing-dev.h @@ -13,6 +13,7 @@ #include #include #include +#include #include #include #include @@ -504,4 +505,13 @@ static inline int bdi_rw_congested(struc (1 << WB_async_congested)); } +extern const char *bdi_unknown_name; + +static inline const char *bdi_dev_name(struct backing_dev_info *bdi) +{ + if (!bdi || !bdi->dev) + return bdi_unknown_name; + return dev_name(bdi->dev); +} + #endif /* _LINUX_BACKING_DEV_H */ --- a/include/trace/events/writeback.h~memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears +++ a/include/trace/events/writeback.h @@ -67,8 +67,8 @@ DECLARE_EVENT_CLASS(writeback_page_templ TP_fast_assign( strscpy_pad(__entry->name, - mapping ? dev_name(inode_to_bdi(mapping->host)->dev) : "(unknown)", - 32); + bdi_dev_name(mapping ? inode_to_bdi(mapping->host) : + NULL), 32); __entry->ino = mapping ? mapping->host->i_ino : 0; __entry->index = page->index; ), @@ -111,8 +111,7 @@ DECLARE_EVENT_CLASS(writeback_dirty_inod struct backing_dev_info *bdi = inode_to_bdi(inode); /* may be called for files on pseudo FSes w/ unregistered bdi */ - strscpy_pad(__entry->name, - bdi->dev ? dev_name(bdi->dev) : "(unknown)", 32); + strscpy_pad(__entry->name, bdi_dev_name(bdi), 32); __entry->ino = inode->i_ino; __entry->state = inode->i_state; __entry->flags = flags; @@ -193,7 +192,7 @@ TRACE_EVENT(inode_foreign_history, ), TP_fast_assign( - strncpy(__entry->name, dev_name(inode_to_bdi(inode)->dev), 32); + strncpy(__entry->name, bdi_dev_name(inode_to_bdi(inode)), 32); __entry->ino = inode->i_ino; __entry->cgroup_ino = __trace_wbc_assign_cgroup(wbc); __entry->history = history; @@ -222,7 +221,7 @@ TRACE_EVENT(inode_switch_wbs, ), TP_fast_assign( - strncpy(__entry->name, dev_name(old_wb->bdi->dev), 32); + strncpy(__entry->name, bdi_dev_name(old_wb->bdi), 32); __entry->ino = inode->i_ino; __entry->old_cgroup_ino = __trace_wb_assign_cgroup(old_wb); __entry->new_cgroup_ino = __trace_wb_assign_cgroup(new_wb); @@ -255,7 +254,7 @@ TRACE_EVENT(track_foreign_dirty, struct address_space *mapping = page_mapping(page); struct inode *inode = mapping ? mapping->host : NULL; - strncpy(__entry->name, dev_name(wb->bdi->dev), 32); + strncpy(__entry->name, bdi_dev_name(wb->bdi), 32); __entry->bdi_id = wb->bdi->id; __entry->ino = inode ? inode->i_ino : 0; __entry->memcg_id = wb->memcg_css->id; @@ -288,7 +287,7 @@ TRACE_EVENT(flush_foreign, ), TP_fast_assign( - strncpy(__entry->name, dev_name(wb->bdi->dev), 32); + strncpy(__entry->name, bdi_dev_name(wb->bdi), 32); __entry->cgroup_ino = __trace_wb_assign_cgroup(wb); __entry->frn_bdi_id = frn_bdi_id; __entry->frn_memcg_id = frn_memcg_id; @@ -318,7 +317,7 @@ DECLARE_EVENT_CLASS(writeback_write_inod TP_fast_assign( strscpy_pad(__entry->name, - dev_name(inode_to_bdi(inode)->dev), 32); + bdi_dev_name(inode_to_bdi(inode)), 32); __entry->ino = inode->i_ino; __entry->sync_mode = wbc->sync_mode; __entry->cgroup_ino = __trace_wbc_assign_cgroup(wbc); @@ -361,9 +360,7 @@ DECLARE_EVENT_CLASS(writeback_work_class __field(ino_t, cgroup_ino) ), TP_fast_assign( - strscpy_pad(__entry->name, - wb->bdi->dev ? dev_name(wb->bdi->dev) : - "(unknown)", 32); + strscpy_pad(__entry->name, bdi_dev_name(wb->bdi), 32); __entry->nr_pages = work->nr_pages; __entry->sb_dev = work->sb ? work->sb->s_dev : 0; __entry->sync_mode = work->sync_mode; @@ -416,7 +413,7 @@ DECLARE_EVENT_CLASS(writeback_class, __field(ino_t, cgroup_ino) ), TP_fast_assign( - strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32); + strscpy_pad(__entry->name, bdi_dev_name(wb->bdi), 32); __entry->cgroup_ino = __trace_wb_assign_cgroup(wb); ), TP_printk("bdi %s: cgroup_ino=%lu", @@ -438,7 +435,7 @@ TRACE_EVENT(writeback_bdi_register, __array(char, name, 32) ), TP_fast_assign( - strscpy_pad(__entry->name, dev_name(bdi->dev), 32); + strscpy_pad(__entry->name, bdi_dev_name(bdi), 32); ), TP_printk("bdi %s", __entry->name @@ -463,7 +460,7 @@ DECLARE_EVENT_CLASS(wbc_class, ), TP_fast_assign( - strscpy_pad(__entry->name, dev_name(bdi->dev), 32); + strscpy_pad(__entry->name, bdi_dev_name(bdi), 32); __entry->nr_to_write = wbc->nr_to_write; __entry->pages_skipped = wbc->pages_skipped; __entry->sync_mode = wbc->sync_mode; @@ -514,7 +511,7 @@ TRACE_EVENT(writeback_queue_io, ), TP_fast_assign( unsigned long *older_than_this = work->older_than_this; - strscpy_pad(__entry->name, dev_name(wb->bdi->dev), 32); + strscpy_pad(__entry->name, bdi_dev_name(wb->bdi), 32); __entry->older = older_than_this ? *older_than_this : 0; __entry->age = older_than_this ? (jiffies - *older_than_this) * 1000 / HZ : -1; @@ -600,7 +597,7 @@ TRACE_EVENT(bdi_dirty_ratelimit, ), TP_fast_assign( - strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32); + strscpy_pad(__entry->bdi, bdi_dev_name(wb->bdi), 32); __entry->write_bw = KBps(wb->write_bandwidth); __entry->avg_write_bw = KBps(wb->avg_write_bandwidth); __entry->dirty_rate = KBps(dirty_rate); @@ -665,7 +662,7 @@ TRACE_EVENT(balance_dirty_pages, TP_fast_assign( unsigned long freerun = (thresh + bg_thresh) / 2; - strscpy_pad(__entry->bdi, dev_name(wb->bdi->dev), 32); + strscpy_pad(__entry->bdi, bdi_dev_name(wb->bdi), 32); __entry->limit = global_wb_domain.dirty_limit; __entry->setpoint = (global_wb_domain.dirty_limit + @@ -726,7 +723,7 @@ TRACE_EVENT(writeback_sb_inodes_requeue, TP_fast_assign( strscpy_pad(__entry->name, - dev_name(inode_to_bdi(inode)->dev), 32); + bdi_dev_name(inode_to_bdi(inode)), 32); __entry->ino = inode->i_ino; __entry->state = inode->i_state; __entry->dirtied_when = inode->dirtied_when; @@ -800,7 +797,7 @@ DECLARE_EVENT_CLASS(writeback_single_ino TP_fast_assign( strscpy_pad(__entry->name, - dev_name(inode_to_bdi(inode)->dev), 32); + bdi_dev_name(inode_to_bdi(inode)), 32); __entry->ino = inode->i_ino; __entry->state = inode->i_state; __entry->dirtied_when = inode->dirtied_when; --- a/mm/backing-dev.c~memcg-fix-a-crash-in-wb_workfn-when-a-device-disappears +++ a/mm/backing-dev.c @@ -21,6 +21,7 @@ struct backing_dev_info noop_backing_dev EXPORT_SYMBOL_GPL(noop_backing_dev_info); static struct class *bdi_class; +const char *bdi_unknown_name = "(unknown)"; /* * bdi_lock protects bdi_tree and updates to bdi_list. bdi_list has RCU