linux-kernel - Re: [PATCH] nilfs2: fix state management in error path of log writing function

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Message-ID: <CAKFNMomFfeeXmeATyG2jARXqvodms+P89TPmcxF70MWdPz2_wA@mail.gmail.com>
Date: Mon, 12 Aug 2024 04:41:35 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-nilfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nilfs2: fix state management in error path of log writing function

On Thu, Aug 8, 2024 at 8:07 AM Ryusuke Konishi wrote:
>
> After commit a694291a6211 ("nilfs2: separate wait function from
> nilfs_segctor_write") was applied, the log writing function
> nilfs_segctor_do_construct() was able to issue I/O requests
> continuously even if user data blocks were split into multiple logs
> across segments, but two potential flaws were introduced in its error
> handling.
>
> First, if nilfs_segctor_begin_construction() fails while creating the
> second or subsequent logs, the log writing function returns without
> calling nilfs_segctor_abort_construction(), so the writeback flag set
> on pages/folios will remain uncleared.  This causes page cache
> operations to hang waiting for the writeback flag.  For example,
> truncate_inode_pages_final(), which is called via nilfs_evict_inode()
> when an inode is evicted from memory, will hang.
>
> Second, the NILFS_I_COLLECTED flag set on normal inodes remain
> uncleared.  As a result, if the next log write involves checkpoint
> creation, that's fine, but if a partial log write is performed that
> does not, inodes with NILFS_I_COLLECTED set are erroneously removed
> from the "sc_dirty_files" list, and their data and b-tree blocks may
> not be written to the device, corrupting the block mapping.
>
> Fix these issues by correcting the jump destination of the error
> branch in nilfs_segctor_do_construct() and the condition for calling
> nilfs_redirty_inodes(), which clears the NILFS_I_COLLECTED flag.
>
> Signed-off-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
> Fixes: a694291a6211 ("nilfs2: separate wait function from nilfs_segctor_write")
> Tested-by: Ryusuke Konishi <konishi.ryusuke@...il.com>
> Cc: stable@...r.kernel.org
> ---
> Hi Andrew, please apply this as a bug fix.
>
> This fixes error path flaws of the log writing function that was
> discovered during error injection testing, which could lead to a hang
> due to the writeback flag not being cleared on folios, and potential
> filesystem corruption due to missing blocks in the log after an error.
>
> Thanks,
> Ryusuke Konishi

Andrew, please stop sending this patch upstream.

I found a problem with changing the error path in this patch in
another error injection test, so I would like to create a revised
version.

The other two bug fix patches I have sent will not be affected.

Thanks,
Ryusuke Konishi

>
>  fs/nilfs2/segment.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
> index 0ca3110d6386..8b3225bd08ed 100644
> --- a/fs/nilfs2/segment.c
> +++ b/fs/nilfs2/segment.c
> @@ -2056,7 +2056,7 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
>
>                 err = nilfs_segctor_begin_construction(sci, nilfs);
>                 if (unlikely(err))
> -                       goto out;
> +                       goto failed;
>
>                 /* Update time stamp */
>                 sci->sc_seg_ctime = ktime_get_real_seconds();
> @@ -2120,10 +2120,9 @@ static int nilfs_segctor_do_construct(struct nilfs_sc_info *sci, int mode)
>         return err;
>
>   failed_to_write:
> -       if (sci->sc_stage.flags & NILFS_CF_IFILE_STARTED)
> -               nilfs_redirty_inodes(&sci->sc_dirty_files);
> -
>   failed:
> +       if (mode == SC_LSEG_SR && nilfs_sc_cstage_get(sci) >= NILFS_ST_IFILE)
> +               nilfs_redirty_inodes(&sci->sc_dirty_files);
>         if (nilfs_doing_gc())
>                 nilfs_redirty_inodes(&sci->sc_gc_inodes);
>         nilfs_segctor_abort_construction(sci, nilfs, err);
> --
> 2.34.1
>