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Tue, 16 Jul 2024 15:47:06 +0800 Received: from mtkmbs13n2.mediatek.inc (172.21.101.108) by MTKMBS14N1.mediatek.inc (172.21.101.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1118.26; Tue, 16 Jul 2024 15:47:02 +0800 Received: from mtksdccf07.mediatek.inc (172.21.84.99) by mtkmbs13n2.mediatek.inc (172.21.101.73) with Microsoft SMTP Server id 15.2.1118.26 via Frontend Transport; Tue, 16 Jul 2024 15:47:02 +0800 From: boy.wu To: Tejun Heo , Josef Bacik , Jens Axboe CC: Matthias Brugger , AngeloGioacchino Del Regno , Boris Burkov , , , , , , , Boy Wu Subject: [PATCH] blk-cgroup: Replace u64 sync with spinlock for iostat update Date: Tue, 16 Jul 2024 15:46:53 +0800 Message-ID: <20240716074653.22524-1-boy.wu@mediatek.com> X-Mailer: git-send-email 2.18.0 Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-TM-AS-Product-Ver: SMEX-14.0.0.3152-9.1.1006-23728.005 X-TM-AS-Result: No-10--11.866300-8.000000 X-TMASE-MatchedRID: aeJu7N9qZHyZtBi01n3C9xafLXbshfogcx5k3wffojOHwGEm+CpYGTEG FjeZwyRUzbrWhbT2b8cTMOv2lZG8w2zFfXEzaNt8wCZxkTHxccn64i5lgawyBFSOymiJfTYXZmL HoWzm2fSMZBHIGOaSwOKOmN63egZIkKjL2IOi2LBbuDP8ZuCmXgApx/9nOtgkVo+424uIBNJYTM 99NlfBm1EXNKIgpuQj+9p3HcFJM3mVhIWL9FEuNwwfhKwa9GwDgGa+oYp5i6qgWMz+iaWIIaPFj JEFr+olwXCBO/GKkVqOhzOa6g8KrUiBZ6mmQX3xiIMgDE0zxa/IQ+RZPevUbELozoV1kXEbSPck h7/tXqI= X-TM-AS-User-Approved-Sender: No X-TM-AS-User-Blocked-Sender: No X-TMASE-Result: 10--11.866300-8.000000 X-TMASE-Version: SMEX-14.0.0.3152-9.1.1006-23728.005 X-TM-SNTS-SMTP: E00DA929F0B966481D5D967B554312843F43A8CF74639FB456D70D4308E86AB62000:8 X-MTK: N From: Boy Wu In 32bit SMP systems, if multiple CPUs call blkcg_print_stat, it may cause blkcg_fill_root_iostats to have a concurrent problem on the seqlock in u64_stats_update, which will cause a deadlock on u64_stats_fetch_begin in blkcg_print_one_stat. Thus, replace u64 sync with spinlock to protect iostat update. Fixes: ef45fe470e1e ("blk-cgroup: show global disk stats in root cgroup io.stat") Signed-off-by: Boy Wu --- Change in v2: - update commit message - Remove u64_sync - Replace spin_lock_irq with guard statement - Replace blkg->q->queue_lock with blkg_stat_lock Change in v3: - update commit message - Add spinlock in blkg_iostat_set structure - Replace all u64_sync with spinlock for iostat - Replace blkg_stat_lock with iostat.spinlock --- block/blk-cgroup.c | 62 +++++++++++++++++++--------------------------- block/blk-cgroup.h | 1 + 2 files changed, 26 insertions(+), 37 deletions(-) diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 37e6cc91d576..4b66f37c45a0 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -329,7 +329,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk, INIT_WORK(&blkg->async_bio_work, blkg_async_bio_workfn); #endif - u64_stats_init(&blkg->iostat.sync); + spin_lock_init(&blkg->iostat.spinlock); for_each_possible_cpu(cpu) { u64_stats_init(&per_cpu_ptr(blkg->iostat_cpu, cpu)->sync); per_cpu_ptr(blkg->iostat_cpu, cpu)->blkg = blkg; @@ -995,15 +995,13 @@ static void blkcg_iostat_update(struct blkcg_gq *blkg, struct blkg_iostat *cur, struct blkg_iostat *last) { struct blkg_iostat delta; - unsigned long flags; /* propagate percpu delta to global */ - flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync); + guard(spinlock_irqsave)(&blkg->iostat.spinlock); blkg_iostat_set(&delta, cur); blkg_iostat_sub(&delta, last); blkg_iostat_add(&blkg->iostat.cur, &delta); blkg_iostat_add(last, &delta); - u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags); } static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) @@ -1034,7 +1032,6 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) struct blkcg_gq *blkg = bisc->blkg; struct blkcg_gq *parent = blkg->parent; struct blkg_iostat cur; - unsigned int seq; /* * Order assignment of `next_bisc` from `bisc->lnode.next` in @@ -1051,10 +1048,8 @@ static void __blkcg_rstat_flush(struct blkcg *blkcg, int cpu) goto propagate_up; /* propagate up to parent only */ /* fetch the current per-cpu values */ - do { - seq = u64_stats_fetch_begin(&bisc->sync); + scoped_guard(spinlock_irqsave, &bisc->spinlock) blkg_iostat_set(&cur, &bisc->cur); - } while (u64_stats_fetch_retry(&bisc->sync, seq)); blkcg_iostat_update(blkg, &cur, &bisc->last); @@ -1112,7 +1107,6 @@ static void blkcg_fill_root_iostats(void) struct blkcg_gq *blkg = bdev->bd_disk->queue->root_blkg; struct blkg_iostat tmp; int cpu; - unsigned long flags; memset(&tmp, 0, sizeof(tmp)); for_each_possible_cpu(cpu) { @@ -1134,9 +1128,8 @@ static void blkcg_fill_root_iostats(void) cpu_dkstats->sectors[STAT_DISCARD] << 9; } - flags = u64_stats_update_begin_irqsave(&blkg->iostat.sync); + guard(spinlock_irqsave)(&blkg->iostat.spinlock); blkg_iostat_set(&blkg->iostat.cur, &tmp); - u64_stats_update_end_irqrestore(&blkg->iostat.sync, flags); } } @@ -1145,7 +1138,6 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s) struct blkg_iostat_set *bis = &blkg->iostat; u64 rbytes, wbytes, rios, wios, dbytes, dios; const char *dname; - unsigned seq; int i; if (!blkg->online) @@ -1157,16 +1149,14 @@ static void blkcg_print_one_stat(struct blkcg_gq *blkg, struct seq_file *s) seq_printf(s, "%s ", dname); - do { - seq = u64_stats_fetch_begin(&bis->sync); - + scoped_guard(spinlock_irqsave, &bis->spinlock) { rbytes = bis->cur.bytes[BLKG_IOSTAT_READ]; wbytes = bis->cur.bytes[BLKG_IOSTAT_WRITE]; dbytes = bis->cur.bytes[BLKG_IOSTAT_DISCARD]; rios = bis->cur.ios[BLKG_IOSTAT_READ]; wios = bis->cur.ios[BLKG_IOSTAT_WRITE]; dios = bis->cur.ios[BLKG_IOSTAT_DISCARD]; - } while (u64_stats_fetch_retry(&bis->sync, seq)); + } if (rbytes || wbytes || rios || wios) { seq_printf(s, "rbytes=%llu wbytes=%llu rios=%llu wios=%llu dbytes=%llu dios=%llu", @@ -2141,7 +2131,6 @@ void blk_cgroup_bio_start(struct bio *bio) struct blkcg *blkcg = bio->bi_blkg->blkcg; int rwd = blk_cgroup_io_type(bio), cpu; struct blkg_iostat_set *bis; - unsigned long flags; if (!cgroup_subsys_on_dfl(io_cgrp_subsys)) return; @@ -2152,30 +2141,29 @@ void blk_cgroup_bio_start(struct bio *bio) cpu = get_cpu(); bis = per_cpu_ptr(bio->bi_blkg->iostat_cpu, cpu); - flags = u64_stats_update_begin_irqsave(&bis->sync); - - /* - * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split - * bio and we would have already accounted for the size of the bio. - */ - if (!bio_flagged(bio, BIO_CGROUP_ACCT)) { - bio_set_flag(bio, BIO_CGROUP_ACCT); - bis->cur.bytes[rwd] += bio->bi_iter.bi_size; - } - bis->cur.ios[rwd]++; + scoped_guard(spinlock_irqsave, &bis->spinlock) { + /* + * If the bio is flagged with BIO_CGROUP_ACCT it means this is a split + * bio and we would have already accounted for the size of the bio. + */ + if (!bio_flagged(bio, BIO_CGROUP_ACCT)) { + bio_set_flag(bio, BIO_CGROUP_ACCT); + bis->cur.bytes[rwd] += bio->bi_iter.bi_size; + } + bis->cur.ios[rwd]++; - /* - * If the iostat_cpu isn't in a lockless list, put it into the - * list to indicate that a stat update is pending. - */ - if (!READ_ONCE(bis->lqueued)) { - struct llist_head *lhead = this_cpu_ptr(blkcg->lhead); + /* + * If the iostat_cpu isn't in a lockless list, put it into the + * list to indicate that a stat update is pending. + */ + if (!READ_ONCE(bis->lqueued)) { + struct llist_head *lhead = this_cpu_ptr(blkcg->lhead); - llist_add(&bis->lnode, lhead); - WRITE_ONCE(bis->lqueued, true); + llist_add(&bis->lnode, lhead); + WRITE_ONCE(bis->lqueued, true); + } } - u64_stats_update_end_irqrestore(&bis->sync, flags); cgroup_rstat_updated(blkcg->css.cgroup, cpu); put_cpu(); } diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h index bd472a30bc61..b9544969a131 100644 --- a/block/blk-cgroup.h +++ b/block/blk-cgroup.h @@ -44,6 +44,7 @@ struct blkg_iostat { }; struct blkg_iostat_set { + spinlock_t spinlock; struct u64_stats_sync sync; struct blkcg_gq *blkg; struct llist_node lnode;