linux-kernel - [PATCH AUTOSEL 5.18 22/22] ext4: correct the judgment of BUG in ext4_mb_normalize

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Date:   Tue, 21 Jun 2022 16:49:28 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Baokun Li <libaokun1@...wei.com>,
        Ritesh Harjani <ritesh.list@...il.com>,
        Theodore Ts'o <tytso@....edu>, Sasha Levin <sashal@...nel.org>,
        adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org
Subject: [PATCH AUTOSEL 5.18 22/22] ext4: correct the judgment of BUG in ext4_mb_normalize_request

From: Baokun Li <libaokun1@...wei.com>

[ Upstream commit cf4ff938b47fc5c00b0ccce53a3b50eca9b32281 ]

ext4_mb_normalize_request() can move logical start of allocated blocks
to reduce fragmentation and better utilize preallocation. However logical
block requested as a start of allocation (ac->ac_o_ex.fe_logical) should
always be covered by allocated blocks so we should check that by
modifying and to or in the assertion.

Signed-off-by: Baokun Li <libaokun1@...wei.com>
Reviewed-by: Ritesh Harjani <ritesh.list@...il.com>
Link: https://lore.kernel.org/r/20220528110017.354175-3-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@....edu>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/ext4/mballoc.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 87d85ce04d58..2ab01cbc0936 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4179,7 +4179,22 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
 	}
 	rcu_read_unlock();
 
-	if (start + size <= ac->ac_o_ex.fe_logical &&
+	/*
+	 * In this function "start" and "size" are normalized for better
+	 * alignment and length such that we could preallocate more blocks.
+	 * This normalization is done such that original request of
+	 * ac->ac_o_ex.fe_logical & fe_len should always lie within "start" and
+	 * "size" boundaries.
+	 * (Note fe_len can be relaxed since FS block allocation API does not
+	 * provide gurantee on number of contiguous blocks allocation since that
+	 * depends upon free space left, etc).
+	 * In case of inode pa, later we use the allocated blocks
+	 * [pa_start + fe_logical - pa_lstart, fe_len/size] from the preallocated
+	 * range of goal/best blocks [start, size] to put it at the
+	 * ac_o_ex.fe_logical extent of this inode.
+	 * (See ext4_mb_use_inode_pa() for more details)
+	 */
+	if (start + size <= ac->ac_o_ex.fe_logical ||
 			start > ac->ac_o_ex.fe_logical) {
 		ext4_msg(ac->ac_sb, KERN_ERR,
 			 "start %lu, size %lu, fe_logical %lu",
-- 
2.35.1