159611cef0
The patch from commit e5731f4 ("backport fix for managing block flush
queue list") caused some fallout when used with LVM on root, as that
uses some rather odd (but previously working fine) PREFLUSH
| POSTFLUSH format that was now causing the list to be used without
being initialized, resulting in freezes.
Link: https://lore.kernel.org/all/20240608143115.972486-1-chengming.zhou@linux.dev/
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
65 lines
2.8 KiB
Diff
65 lines
2.8 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Chengming Zhou <chengming.zhou@linux.dev>
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Date: Sat, 8 Jun 2024 22:31:15 +0800
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Subject: [PATCH] block: fix request.queuelist usage in flush
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Friedrich Weber reported a kernel crash problem and bisected to commit
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81ada09cc25e ("blk-flush: reuse rq queuelist in flush state machine").
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The root cause is that we use "list_move_tail(&rq->queuelist, pending)"
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in the PREFLUSH/POSTFLUSH sequences. But rq->queuelist.next == xxx since
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it's popped out from plug->cached_rq in __blk_mq_alloc_requests_batch().
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We don't initialize its queuelist just for this first request, although
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the queuelist of all later popped requests will be initialized.
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Fix it by changing to use "list_add_tail(&rq->queuelist, pending)" so
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rq->queuelist doesn't need to be initialized. It should be ok since rq
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can't be on any list when PREFLUSH or POSTFLUSH, has no move actually.
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Please note the commit 81ada09cc25e ("blk-flush: reuse rq queuelist in
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flush state machine") also has another requirement that no drivers would
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touch rq->queuelist after blk_mq_end_request() since we will reuse it to
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add rq to the post-flush pending list in POSTFLUSH. If this is not true,
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we will have to revert that commit IMHO.
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This updated version adds "list_del_init(&rq->queuelist)" in flush rq
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callback since the dm layer may submit request of a weird invalid format
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(REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH), which causes double list_add
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if without this "list_del_init(&rq->queuelist)". The weird invalid format
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problem should be fixed in dm layer.
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Reported-by: Friedrich Weber <f.weber@proxmox.com>
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Closes: https://lore.kernel.org/lkml/14b89dfb-505c-49f7-aebb-01c54451db40@proxmox.com/
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Closes: https://lore.kernel.org/lkml/c9d03ff7-27c5-4ebd-b3f6-5a90d96f35ba@proxmox.com/
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Fixes: 81ada09cc25e ("blk-flush: reuse rq queuelist in flush state machine")
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Cc: Christoph Hellwig <hch@lst.de>
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Cc: ming.lei@redhat.com
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Cc: bvanassche@acm.org
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Tested-by: Friedrich Weber <f.weber@proxmox.com>
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Signed-off-by: Chengming Zhou <chengming.zhou@linux.dev>
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---
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block/blk-flush.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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diff --git a/block/blk-flush.c b/block/blk-flush.c
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index 3f4d41952ef2..d72b57898b23 100644
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--- a/block/blk-flush.c
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+++ b/block/blk-flush.c
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@@ -183,7 +183,7 @@ static void blk_flush_complete_seq(struct request *rq,
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/* queue for flush */
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if (list_empty(pending))
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fq->flush_pending_since = jiffies;
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- list_move_tail(&rq->queuelist, pending);
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+ list_add_tail(&rq->queuelist, pending);
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break;
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case REQ_FSEQ_DATA:
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@@ -261,6 +261,7 @@ static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
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unsigned int seq = blk_flush_cur_seq(rq);
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BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
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+ list_del_init(&rq->queuelist);
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blk_flush_complete_seq(rq, fq, seq, error);
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}
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