linux-ext4 - Re: [PATCH 1/3] quota: Prevent memory allocation recursion while holding dq

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Date:   Mon, 6 Jun 2022 10:03:34 +0200
From:   Jan Kara <jack@...e.cz>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     Jan Kara <jack@...e.com>, tytso@....edu,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 1/3] quota: Prevent memory allocation recursion while
 holding dq_lock

On Sun 05-06-22 15:38:13, Matthew Wilcox (Oracle) wrote:
> As described in commit 02117b8ae9c0 ("f2fs: Set GF_NOFS in
> read_cache_page_gfp while doing f2fs_quota_read"), we must not enter
> filesystem reclaim while holding the dq_lock.  Prevent this more generally
> by using memalloc_nofs_save() while holding the lock.
> 
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>

This is definitely a good cleanup to have and seems mostly unrelated to the
rest. I'll take it rightaway into my tree. Thanks for the patch!

								Honza

> ---
>  fs/quota/dquot.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
> index a74aef99bd3d..cdb22d6d7488 100644
> --- a/fs/quota/dquot.c
> +++ b/fs/quota/dquot.c
> @@ -425,9 +425,11 @@ EXPORT_SYMBOL(mark_info_dirty);
>  int dquot_acquire(struct dquot *dquot)
>  {
>  	int ret = 0, ret2 = 0;
> +	unsigned int memalloc;
>  	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
>  
>  	mutex_lock(&dquot->dq_lock);
> +	memalloc = memalloc_nofs_save();
>  	if (!test_bit(DQ_READ_B, &dquot->dq_flags)) {
>  		ret = dqopt->ops[dquot->dq_id.type]->read_dqblk(dquot);
>  		if (ret < 0)
> @@ -458,6 +460,7 @@ int dquot_acquire(struct dquot *dquot)
>  	smp_mb__before_atomic();
>  	set_bit(DQ_ACTIVE_B, &dquot->dq_flags);
>  out_iolock:
> +	memalloc_nofs_restore(memalloc);
>  	mutex_unlock(&dquot->dq_lock);
>  	return ret;
>  }
> @@ -469,9 +472,11 @@ EXPORT_SYMBOL(dquot_acquire);
>  int dquot_commit(struct dquot *dquot)
>  {
>  	int ret = 0;
> +	unsigned int memalloc;
>  	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
>  
>  	mutex_lock(&dquot->dq_lock);
> +	memalloc = memalloc_nofs_save();
>  	if (!clear_dquot_dirty(dquot))
>  		goto out_lock;
>  	/* Inactive dquot can be only if there was error during read/init
> @@ -481,6 +486,7 @@ int dquot_commit(struct dquot *dquot)
>  	else
>  		ret = -EIO;
>  out_lock:
> +	memalloc_nofs_restore(memalloc);
>  	mutex_unlock(&dquot->dq_lock);
>  	return ret;
>  }
> @@ -492,9 +498,11 @@ EXPORT_SYMBOL(dquot_commit);
>  int dquot_release(struct dquot *dquot)
>  {
>  	int ret = 0, ret2 = 0;
> +	unsigned int memalloc;
>  	struct quota_info *dqopt = sb_dqopt(dquot->dq_sb);
>  
>  	mutex_lock(&dquot->dq_lock);
> +	memalloc = memalloc_nofs_save();
>  	/* Check whether we are not racing with some other dqget() */
>  	if (dquot_is_busy(dquot))
>  		goto out_dqlock;
> @@ -510,6 +518,7 @@ int dquot_release(struct dquot *dquot)
>  	}
>  	clear_bit(DQ_ACTIVE_B, &dquot->dq_flags);
>  out_dqlock:
> +	memalloc_nofs_restore(memalloc);
>  	mutex_unlock(&dquot->dq_lock);
>  	return ret;
>  }
> -- 
> 2.35.1
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR