From patchwork Sun May 22 17:07:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Coly Li X-Patchwork-Id: 12858288 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 45F0EC433FE for ; Sun, 22 May 2022 17:08:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349656AbiEVRID (ORCPT ); Sun, 22 May 2022 13:08:03 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232802AbiEVRID (ORCPT ); Sun, 22 May 2022 13:08:03 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01ED13AA41; Sun, 22 May 2022 10:08:02 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id B3E5B21A72; Sun, 22 May 2022 17:08:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1653239280; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wmJpe9/Kua8zJtz04nyJuieA4qrmKJ7yZERYmqpEk9U=; b=uWoeNullntL857Y+VVgdC2hvcgRPJ/LqtnmDDQl2hmZD3Jr+lrKT8aOe061N6O04DlEU+M leic693DAyw3bE5j2D2aDS/XP/nDjx3UrXmZC+KFd/w5DxDpWBtRCJgcthoc64APFGuAm+ UUBU2jlG+xGb2BCbFBieUzpNh8nWsoc= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1653239280; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wmJpe9/Kua8zJtz04nyJuieA4qrmKJ7yZERYmqpEk9U=; b=VdCdMOvkhGgESLdRGDqvNgMACvqs1HMBvspPl45uYHQN5OcusY5AgB2DqihNAfr9BLCwL0 d127tlqJY2S+52DA== Received: from localhost.localdomain (colyli.tcp.ovpn1.nue.suse.de [10.163.16.22]) by relay2.suse.de (Postfix) with ESMTP id 4D26A2C141; Sun, 22 May 2022 17:07:52 +0000 (UTC) From: Coly Li To: axboe@kernel.dk Cc: linux-bcache@vger.kernel.org, linux-block@vger.kernel.org, Coly Li , Nikhil Kshirsagar , stable@vger.kernel.org Subject: [PATCH 4/4] bcache: avoid journal no-space deadlock by reserving 1 journal bucket Date: Mon, 23 May 2022 01:07:36 +0800 Message-Id: <20220522170736.6582-5-colyli@suse.de> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20220522170736.6582-1-colyli@suse.de> References: <20220522170736.6582-1-colyli@suse.de> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org The journal no-space deadlock was reported time to time. Such deadlock can happen in the following situation. When all journal buckets are fully filled by active jset with heavy write I/O load, the cache set registration (after a reboot) will load all active jsets and inserting them into the btree again (which is called journal replay). If a journaled bkey is inserted into a btree node and results btree node split, new journal request might be triggered. For example, the btree grows one more level after the node split, then the root node record in cache device super block will be upgrade by bch_journal_meta() from bch_btree_set_root(). But there is no space in journal buckets, the journal replay has to wait for new journal bucket to be reclaimed after at least one journal bucket replayed. This is one example that how the journal no-space deadlock happens. The solution to avoid the deadlock is to reserve 1 journal bucket in run time, and only permit the reserved journal bucket to be used during cache set registration procedure for things like journal replay. Then the journal space will never be fully filled, there is no chance for journal no-space deadlock to happen anymore. This patch adds a new member "bool do_reserve" in struct journal, it is inititalized to 0 (false) when struct journal is allocated, and set to 1 (true) by bch_journal_space_reserve() when all initialization done in run_cache_set(). In the run time when journal_reclaim() tries to allocate a new journal bucket, free_journal_buckets() is called to check whether there are enough free journal buckets to use. If there is only 1 free journal bucket and journal->do_reserve is 1 (true), the last bucket is reserved and free_journal_buckets() will return 0 to indicate no free journal bucket. Then journal_reclaim() will give up, and try next time to see whetheer there is free journal bucket to allocate. By this method, there is always 1 jouranl bucket reserved in run time. During the cache set registration, journal->do_reserve is 0 (false), so the reserved journal bucket can be used to avoid the no-space deadlock. Reported-by: Nikhil Kshirsagar Signed-off-by: Coly Li Cc: stable@vger.kernel.org --- drivers/md/bcache/journal.c | 31 ++++++++++++++++++++++++++----- drivers/md/bcache/journal.h | 2 ++ drivers/md/bcache/super.c | 1 + 3 files changed, 29 insertions(+), 5 deletions(-) diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c index df5347ea450b..e5da469a4235 100644 --- a/drivers/md/bcache/journal.c +++ b/drivers/md/bcache/journal.c @@ -405,6 +405,11 @@ int bch_journal_replay(struct cache_set *s, struct list_head *list) return ret; } +void bch_journal_space_reserve(struct journal *j) +{ + j->do_reserve = true; +} + /* Journalling */ static void btree_flush_write(struct cache_set *c) @@ -621,12 +626,30 @@ static void do_journal_discard(struct cache *ca) } } +static unsigned int free_journal_buckets(struct cache_set *c) +{ + struct journal *j = &c->journal; + struct cache *ca = c->cache; + struct journal_device *ja = &c->cache->journal; + unsigned int n; + + /* In case njournal_buckets is not power of 2 */ + if (ja->cur_idx >= ja->discard_idx) + n = ca->sb.njournal_buckets + ja->discard_idx - ja->cur_idx; + else + n = ja->discard_idx - ja->cur_idx; + + if (n > (1 + j->do_reserve)) + return n - (1 + j->do_reserve); + + return 0; +} + static void journal_reclaim(struct cache_set *c) { struct bkey *k = &c->journal.key; struct cache *ca = c->cache; uint64_t last_seq; - unsigned int next; struct journal_device *ja = &ca->journal; atomic_t p __maybe_unused; @@ -649,12 +672,10 @@ static void journal_reclaim(struct cache_set *c) if (c->journal.blocks_free) goto out; - next = (ja->cur_idx + 1) % ca->sb.njournal_buckets; - /* No space available on this device */ - if (next == ja->discard_idx) + if (!free_journal_buckets(c)) goto out; - ja->cur_idx = next; + ja->cur_idx = (ja->cur_idx + 1) % ca->sb.njournal_buckets; k->ptr[0] = MAKE_PTR(0, bucket_to_sector(c, ca->sb.d[ja->cur_idx]), ca->sb.nr_this_dev); diff --git a/drivers/md/bcache/journal.h b/drivers/md/bcache/journal.h index f2ea34d5f431..cd316b4a1e95 100644 --- a/drivers/md/bcache/journal.h +++ b/drivers/md/bcache/journal.h @@ -105,6 +105,7 @@ struct journal { spinlock_t lock; spinlock_t flush_write_lock; bool btree_flushing; + bool do_reserve; /* used when waiting because the journal was full */ struct closure_waitlist wait; struct closure io; @@ -182,5 +183,6 @@ int bch_journal_replay(struct cache_set *c, struct list_head *list); void bch_journal_free(struct cache_set *c); int bch_journal_alloc(struct cache_set *c); +void bch_journal_space_reserve(struct journal *j); #endif /* _BCACHE_JOURNAL_H */ diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c index bf3de149d3c9..2bb55278d22d 100644 --- a/drivers/md/bcache/super.c +++ b/drivers/md/bcache/super.c @@ -2128,6 +2128,7 @@ static int run_cache_set(struct cache_set *c) flash_devs_run(c); + bch_journal_space_reserve(&c->journal); set_bit(CACHE_SET_RUNNING, &c->flags); return 0; err: