From patchwork Tue Oct 19 13:41:55 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andreas Gruenbacher X-Patchwork-Id: 12569919 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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 292CCC4332F for ; Tue, 19 Oct 2021 13:43:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 12F146138B for ; Tue, 19 Oct 2021 13:43:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236011AbhJSNpP (ORCPT ); Tue, 19 Oct 2021 09:45:15 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:24032 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235970AbhJSNpA (ORCPT ); Tue, 19 Oct 2021 09:45:00 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1634650967; h=from:from:reply-to:subject:subject: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=7tOQbj2Gm69Jj+vC/ygquxAoG/xp6fXc1aePeCdCs3M=; b=b18I8giiHCE//LbE+v+7cmlyDmg5IpAYntoRGQpOeGLfxpxCkQwvr/ISj4u4EnKSdVBtuY oZhlyeUyfRVCp+lstopMGjp3jJVPr/VNIOa37jXy3oqKg2KdmI3LE7DDqtJ8DkbkNavCTq UIp7kPgfJWNGWfukuaBKx4ea9eageB0= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-204-PBcGwx-sOJq34hBNABWYKA-1; Tue, 19 Oct 2021 09:42:43 -0400 X-MC-Unique: PBcGwx-sOJq34hBNABWYKA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32D568066F8; Tue, 19 Oct 2021 13:42:42 +0000 (UTC) Received: from max.com (unknown [10.40.193.143]) by smtp.corp.redhat.com (Postfix) with ESMTP id 293B110016FC; Tue, 19 Oct 2021 13:42:35 +0000 (UTC) From: Andreas Gruenbacher To: Linus Torvalds , Catalin Marinas Cc: Alexander Viro , Christoph Hellwig , "Darrick J. Wong" , Paul Mackerras , Jan Kara , Matthew Wilcox , cluster-devel@redhat.com, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, ocfs2-devel@oss.oracle.com, kvm-ppc@vger.kernel.org, linux-btrfs@vger.kernel.org, Bob Peterson , Andreas Gruenbacher Subject: [PATCH v8 08/17] gfs2: Introduce flag for glock holder auto-demotion Date: Tue, 19 Oct 2021 15:41:55 +0200 Message-Id: <20211019134204.3382645-9-agruenba@redhat.com> In-Reply-To: <20211019134204.3382645-1-agruenba@redhat.com> References: <20211019134204.3382645-1-agruenba@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org From: Bob Peterson This patch introduces a new HIF_MAY_DEMOTE flag and infrastructure that will allow glocks to be demoted automatically on locking conflicts. When a locking request comes in that isn't compatible with the locking state of an active holder and that holder has the HIF_MAY_DEMOTE flag set, the holder will be demoted before the incoming locking request is granted. Note that this mechanism demotes active holders (with the HIF_HOLDER flag set), while before we were only demoting glocks without any active holders. This allows processes to keep hold of locks that may form a cyclic locking dependency; the core glock logic will then break those dependencies in case a conflicting locking request occurs. We'll use this to avoid giving up the inode glock proactively before faulting in pages. Processes that allow a glock holder to be taken away indicate this by calling gfs2_holder_allow_demote(), which sets the HIF_MAY_DEMOTE flag. Later, they call gfs2_holder_disallow_demote() to clear the flag again, and then they check if their holder is still queued: if it is, they are still holding the glock; if it isn't, they can re-acquire the glock (or abort). Signed-off-by: Bob Peterson Signed-off-by: Andreas Gruenbacher --- fs/gfs2/glock.c | 215 +++++++++++++++++++++++++++++++++++++++-------- fs/gfs2/glock.h | 20 +++++ fs/gfs2/incore.h | 1 + 3 files changed, 200 insertions(+), 36 deletions(-) diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index f24db2ececfb..6a595ba5a979 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -58,6 +58,7 @@ struct gfs2_glock_iter { typedef void (*glock_examiner) (struct gfs2_glock * gl); static void do_xmote(struct gfs2_glock *gl, struct gfs2_holder *gh, unsigned int target); +static void __gfs2_glock_dq(struct gfs2_holder *gh); static struct dentry *gfs2_root; static struct workqueue_struct *glock_workqueue; @@ -197,6 +198,12 @@ static int demote_ok(const struct gfs2_glock *gl) if (gl->gl_state == LM_ST_UNLOCKED) return 0; + /* + * Note that demote_ok is used for the lru process of disposing of + * glocks. For this purpose, we don't care if the glock's holders + * have the HIF_MAY_DEMOTE flag set or not. If someone is using + * them, don't demote. + */ if (!list_empty(&gl->gl_holders)) return 0; if (glops->go_demote_ok) @@ -379,7 +386,7 @@ static void do_error(struct gfs2_glock *gl, const int ret) struct gfs2_holder *gh, *tmp; list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) { - if (test_bit(HIF_HOLDER, &gh->gh_iflags)) + if (!test_bit(HIF_WAIT, &gh->gh_iflags)) continue; if (ret & LM_OUT_ERROR) gh->gh_error = -EIO; @@ -393,6 +400,40 @@ static void do_error(struct gfs2_glock *gl, const int ret) } } +/** + * demote_incompat_holders - demote incompatible demoteable holders + * @gl: the glock we want to promote + * @new_gh: the new holder to be promoted + */ +static void demote_incompat_holders(struct gfs2_glock *gl, + struct gfs2_holder *new_gh) +{ + struct gfs2_holder *gh; + + /* + * Demote incompatible holders before we make ourselves eligible. + * (This holder may or may not allow auto-demoting, but we don't want + * to demote the new holder before it's even granted.) + */ + list_for_each_entry(gh, &gl->gl_holders, gh_list) { + /* + * Since holders are at the front of the list, we stop when we + * find the first non-holder. + */ + if (!test_bit(HIF_HOLDER, &gh->gh_iflags)) + return; + if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags) && + !may_grant(gl, new_gh, gh)) { + /* + * We should not recurse into do_promote because + * __gfs2_glock_dq only calls handle_callback, + * gfs2_glock_add_to_lru and __gfs2_glock_queue_work. + */ + __gfs2_glock_dq(gh); + } + } +} + /** * find_first_holder - find the first "holder" gh * @gl: the glock @@ -411,6 +452,26 @@ static inline struct gfs2_holder *find_first_holder(const struct gfs2_glock *gl) return NULL; } +/** + * find_first_strong_holder - find the first non-demoteable holder + * @gl: the glock + * + * Find the first holder that doesn't have the HIF_MAY_DEMOTE flag set. + */ +static inline struct gfs2_holder +*find_first_strong_holder(struct gfs2_glock *gl) +{ + struct gfs2_holder *gh; + + list_for_each_entry(gh, &gl->gl_holders, gh_list) { + if (!test_bit(HIF_HOLDER, &gh->gh_iflags)) + return NULL; + if (!test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags)) + return gh; + } + return NULL; +} + /** * do_promote - promote as many requests as possible on the current queue * @gl: The glock @@ -425,15 +486,21 @@ __acquires(&gl->gl_lockref.lock) { const struct gfs2_glock_operations *glops = gl->gl_ops; struct gfs2_holder *gh, *tmp, *first_gh; + bool incompat_holders_demoted = false; int ret; - first_gh = find_first_holder(gl); + first_gh = find_first_strong_holder(gl); restart: list_for_each_entry_safe(gh, tmp, &gl->gl_holders, gh_list) { - if (test_bit(HIF_HOLDER, &gh->gh_iflags)) + if (!test_bit(HIF_WAIT, &gh->gh_iflags)) continue; if (may_grant(gl, first_gh, gh)) { + if (!incompat_holders_demoted) { + demote_incompat_holders(gl, first_gh); + incompat_holders_demoted = true; + first_gh = gh; + } if (gh->gh_list.prev == &gl->gl_holders && glops->go_lock) { spin_unlock(&gl->gl_lockref.lock); @@ -459,6 +526,11 @@ __acquires(&gl->gl_lockref.lock) gfs2_holder_wake(gh); continue; } + /* + * If we get here, it means we may not grant this holder for + * some reason. If this holder is the head of the list, it + * means we have a blocked holder at the head, so return 1. + */ if (gh->gh_list.prev == &gl->gl_holders) return 1; do_error(gl, 0); @@ -1373,7 +1445,7 @@ __acquires(&gl->gl_lockref.lock) if (test_bit(GLF_LOCK, &gl->gl_flags)) { struct gfs2_holder *first_gh; - first_gh = find_first_holder(gl); + first_gh = find_first_strong_holder(gl); try_futile = !may_grant(gl, first_gh, gh); } if (test_bit(GLF_INVALIDATE_IN_PROGRESS, &gl->gl_flags)) @@ -1382,7 +1454,8 @@ __acquires(&gl->gl_lockref.lock) list_for_each_entry(gh2, &gl->gl_holders, gh_list) { if (unlikely(gh2->gh_owner_pid == gh->gh_owner_pid && - (gh->gh_gl->gl_ops->go_type != LM_TYPE_FLOCK))) + (gh->gh_gl->gl_ops->go_type != LM_TYPE_FLOCK) && + !test_bit(HIF_MAY_DEMOTE, &gh2->gh_iflags))) goto trap_recursive; if (try_futile && !(gh2->gh_flags & (LM_FLAG_TRY | LM_FLAG_TRY_1CB))) { @@ -1478,51 +1551,83 @@ int gfs2_glock_poll(struct gfs2_holder *gh) return test_bit(HIF_WAIT, &gh->gh_iflags) ? 0 : 1; } -/** - * gfs2_glock_dq - dequeue a struct gfs2_holder from a glock (release a glock) - * @gh: the glock holder - * - */ +static inline bool needs_demote(struct gfs2_glock *gl) +{ + return (test_bit(GLF_DEMOTE, &gl->gl_flags) || + test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags)); +} -void gfs2_glock_dq(struct gfs2_holder *gh) +static void __gfs2_glock_dq(struct gfs2_holder *gh) { struct gfs2_glock *gl = gh->gh_gl; struct gfs2_sbd *sdp = gl->gl_name.ln_sbd; unsigned delay = 0; int fast_path = 0; - spin_lock(&gl->gl_lockref.lock); /* - * If we're in the process of file system withdraw, we cannot just - * dequeue any glocks until our journal is recovered, lest we - * introduce file system corruption. We need two exceptions to this - * rule: We need to allow unlocking of nondisk glocks and the glock - * for our own journal that needs recovery. + * This while loop is similar to function demote_incompat_holders: + * If the glock is due to be demoted (which may be from another node + * or even if this holder is GL_NOCACHE), the weak holders are + * demoted as well, allowing the glock to be demoted. */ - if (test_bit(SDF_WITHDRAW_RECOVERY, &sdp->sd_flags) && - glock_blocked_by_withdraw(gl) && - gh->gh_gl != sdp->sd_jinode_gl) { - sdp->sd_glock_dqs_held++; - spin_unlock(&gl->gl_lockref.lock); - might_sleep(); - wait_on_bit(&sdp->sd_flags, SDF_WITHDRAW_RECOVERY, - TASK_UNINTERRUPTIBLE); - spin_lock(&gl->gl_lockref.lock); - } - if (gh->gh_flags & GL_NOCACHE) - handle_callback(gl, LM_ST_UNLOCKED, 0, false); + while (gh) { + /* + * If we're in the process of file system withdraw, we cannot + * just dequeue any glocks until our journal is recovered, lest + * we introduce file system corruption. We need two exceptions + * to this rule: We need to allow unlocking of nondisk glocks + * and the glock for our own journal that needs recovery. + */ + if (test_bit(SDF_WITHDRAW_RECOVERY, &sdp->sd_flags) && + glock_blocked_by_withdraw(gl) && + gh->gh_gl != sdp->sd_jinode_gl) { + sdp->sd_glock_dqs_held++; + spin_unlock(&gl->gl_lockref.lock); + might_sleep(); + wait_on_bit(&sdp->sd_flags, SDF_WITHDRAW_RECOVERY, + TASK_UNINTERRUPTIBLE); + spin_lock(&gl->gl_lockref.lock); + } + + /* + * This holder should not be cached, so mark it for demote. + * Note: this should be done before the check for needs_demote + * below. + */ + if (gh->gh_flags & GL_NOCACHE) + handle_callback(gl, LM_ST_UNLOCKED, 0, false); + + list_del_init(&gh->gh_list); + clear_bit(HIF_HOLDER, &gh->gh_iflags); + trace_gfs2_glock_queue(gh, 0); + + /* + * If there hasn't been a demote request we are done. + * (Let the remaining holders, if any, keep holding it.) + */ + if (!needs_demote(gl)) { + if (list_empty(&gl->gl_holders)) + fast_path = 1; + break; + } + /* + * If we have another strong holder (we cannot auto-demote) + * we are done. It keeps holding it until it is done. + */ + if (find_first_strong_holder(gl)) + break; - list_del_init(&gh->gh_list); - clear_bit(HIF_HOLDER, &gh->gh_iflags); - if (list_empty(&gl->gl_holders) && - !test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) && - !test_bit(GLF_DEMOTE, &gl->gl_flags)) - fast_path = 1; + /* + * If we have a weak holder at the head of the list, it + * (and all others like it) must be auto-demoted. If there + * are no more weak holders, we exit the while loop. + */ + gh = find_first_holder(gl); + } if (!test_bit(GLF_LFLUSH, &gl->gl_flags) && demote_ok(gl)) gfs2_glock_add_to_lru(gl); - trace_gfs2_glock_queue(gh, 0); if (unlikely(!fast_path)) { gl->gl_lockref.count++; if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) && @@ -1531,6 +1636,19 @@ void gfs2_glock_dq(struct gfs2_holder *gh) delay = gl->gl_hold_time; __gfs2_glock_queue_work(gl, delay); } +} + +/** + * gfs2_glock_dq - dequeue a struct gfs2_holder from a glock (release a glock) + * @gh: the glock holder + * + */ +void gfs2_glock_dq(struct gfs2_holder *gh) +{ + struct gfs2_glock *gl = gh->gh_gl; + + spin_lock(&gl->gl_lockref.lock); + __gfs2_glock_dq(gh); spin_unlock(&gl->gl_lockref.lock); } @@ -1693,6 +1811,7 @@ void gfs2_glock_dq_m(unsigned int num_gh, struct gfs2_holder *ghs) void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state) { + struct gfs2_holder mock_gh = { .gh_gl = gl, .gh_state = state, }; unsigned long delay = 0; unsigned long holdtime; unsigned long now = jiffies; @@ -1707,6 +1826,28 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state) if (test_bit(GLF_REPLY_PENDING, &gl->gl_flags)) delay = gl->gl_hold_time; } + /* + * Note 1: We cannot call demote_incompat_holders from handle_callback + * or gfs2_set_demote due to recursion problems like: gfs2_glock_dq -> + * handle_callback -> demote_incompat_holders -> gfs2_glock_dq + * Plus, we only want to demote the holders if the request comes from + * a remote cluster node because local holder conflicts are resolved + * elsewhere. + * + * Note 2: if a remote node wants this glock in EX mode, lock_dlm will + * request that we set our state to UNLOCKED. Here we mock up a holder + * to make it look like someone wants the lock EX locally. Any SH + * and DF requests should be able to share the lock without demoting. + * + * Note 3: We only want to demote the demoteable holders when there + * are no more strong holders. The demoteable holders might as well + * keep the glock until the last strong holder is done with it. + */ + if (!find_first_strong_holder(gl)) { + if (state == LM_ST_UNLOCKED) + mock_gh.gh_state = LM_ST_EXCLUSIVE; + demote_incompat_holders(gl, &mock_gh); + } handle_callback(gl, state, delay, true); __gfs2_glock_queue_work(gl, delay); spin_unlock(&gl->gl_lockref.lock); @@ -2096,6 +2237,8 @@ static const char *hflags2str(char *buf, u16 flags, unsigned long iflags) *p++ = 'H'; if (test_bit(HIF_WAIT, &iflags)) *p++ = 'W'; + if (test_bit(HIF_MAY_DEMOTE, &iflags)) + *p++ = 'D'; *p = 0; return buf; } diff --git a/fs/gfs2/glock.h b/fs/gfs2/glock.h index 31a8f2f649b5..9012487da4c6 100644 --- a/fs/gfs2/glock.h +++ b/fs/gfs2/glock.h @@ -150,6 +150,8 @@ static inline struct gfs2_holder *gfs2_glock_is_locked_by_me(struct gfs2_glock * list_for_each_entry(gh, &gl->gl_holders, gh_list) { if (!test_bit(HIF_HOLDER, &gh->gh_iflags)) break; + if (test_bit(HIF_MAY_DEMOTE, &gh->gh_iflags)) + continue; if (gh->gh_owner_pid == pid) goto out; } @@ -325,6 +327,24 @@ static inline void glock_clear_object(struct gfs2_glock *gl, void *object) spin_unlock(&gl->gl_lockref.lock); } +static inline void gfs2_holder_allow_demote(struct gfs2_holder *gh) +{ + struct gfs2_glock *gl = gh->gh_gl; + + spin_lock(&gl->gl_lockref.lock); + set_bit(HIF_MAY_DEMOTE, &gh->gh_iflags); + spin_unlock(&gl->gl_lockref.lock); +} + +static inline void gfs2_holder_disallow_demote(struct gfs2_holder *gh) +{ + struct gfs2_glock *gl = gh->gh_gl; + + spin_lock(&gl->gl_lockref.lock); + clear_bit(HIF_MAY_DEMOTE, &gh->gh_iflags); + spin_unlock(&gl->gl_lockref.lock); +} + extern void gfs2_inode_remember_delete(struct gfs2_glock *gl, u64 generation); extern bool gfs2_inode_already_deleted(struct gfs2_glock *gl, u64 generation); diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h index 0fe49770166e..58b7bac501e4 100644 --- a/fs/gfs2/incore.h +++ b/fs/gfs2/incore.h @@ -252,6 +252,7 @@ struct gfs2_lkstats { enum { /* States */ + HIF_MAY_DEMOTE = 1, HIF_HOLDER = 6, /* Set for gh that "holds" the glock */ HIF_WAIT = 10, };