linux-kernel - Re: [PATCH 0/1] ext4: Fix regression in mballoc due to deleted inode PAs in rbtree

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Message-Id: <169011551315.10885.4411764690665517539.b4-ty@mit.edu>
Date:   Sun, 23 Jul 2023 08:32:00 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     linux-ext4@...r.kernel.org, Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Naresh Kamboju <naresh.kamboju@...aro.org>
Subject: Re: [PATCH 0/1] ext4: Fix regression in mballoc due to deleted inode PAs in rbtree


On Sat, 22 Jul 2023 22:45:23 +0530, Ojaswin Mujoo wrote:
> Recently there was a regression found in the mballoc [1] due the existence
> of deleted preallocations(PAs) in the per inode preallocation rbtree.
> Such deleted PAs can occur because ext4_mb_discard_group_preallocations
> traverses the grp->bb_prealloc_list and marks the PAs as deleted without
> taking any inode specific locks like i_data_sem.
> 
> Due to presence of such PAs, we were sometimes missing some of the pa
> entries when traversing the per node rbtree in ext4_mb_use_preallocated.
> Due to this, in some rare conditions we ended up missing a PA that did
> overlap with our original request start. when this happens, we exit
> ext4_mb_use_preallocated and proceed with the allocation. However,
> during ext4_mb_normalize_request() we were hitting a bug on as
> a PA that could satisfy our request already existed. Since normalize
> request was already fixed earlier to account for the deleted PAs we
> actually able to catch it there.
> 
> [...]

Applied, thanks!

[1/1] ext4: Fix rbtree traversal bug in ext4_mb_use_preallocated
      commit: 9d3de7ee192a6a253f475197fe4d2e2af10a731f

Best regards,
-- 
Theodore Ts'o <tytso@....edu>