linux-kernel - Re: [PATCH REVIEW] udf: Fix lock inversion between iprune_mutex and alloc

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Date:	Mon, 18 Aug 2008 14:47:59 +0200
From:	Jan Kara <jack@...e.cz>
To:	Ingo Oeser <ioe-lkml@...eria.de>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH REVIEW] udf: Fix lock inversion between iprune_mutex
	and alloc_mutex

On Thu 14-08-08 20:48:10, Ingo Oeser wrote:
> Hi Jan,
> 
> On Thursday 14 August 2008, Jan Kara wrote:
> > A memory allocation inside alloc_mutex must not recurse back
> > into the filesystem itself because that leads to lock inversion
> > between iprune_mutex and alloc_mutex (and thus to deadlocks - see
> > traces below). Make allocations inside alloc_mutex use GFP_NOFS
> > to avoid this problem.
> 
> What about moving the allocation before taking the mutex?
> That way, we even reduce the lock contention and simplify the failure path.
  Thanks for the idea and the review. Actually, I've checked and
i_alloc_mutex is needed only to update allocation statistics in the
superblock. So we can release i_alloc_mutex earlier before allocating
memory. Actually, I ended up moving the memory allocation as well - even
before the block allocation - to fix the error path cleanup. I'll post
resulting two patches in a moment.

									Honza

> Signed-off-by: Ingo Oeser <ioe-lkml@...eria.de>
> 
> diff --git a/fs/udf/ialloc.c b/fs/udf/ialloc.c
> index eb9cfa2..76446eb 100644
> --- a/fs/udf/ialloc.c
> +++ b/fs/udf/ialloc.c
> @@ -90,6 +90,25 @@ struct inode *udf_new_inode(struct inode *dir, int mode, int *err)
>  		return NULL;
>  	}
>  
> +	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
> +		iinfo->i_efe = 1;
> +		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
> +			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
> +		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
> +					    sizeof(struct extendedFileEntry),
> +					    GFP_KERNEL);
> +	} else {
> +		iinfo->i_efe = 0;
> +		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
> +					    sizeof(struct fileEntry),
> +					    GFP_KERNEL);
> +	}
> +	if (!iinfo->i_ext.i_data) {
> +		iput(inode);
> +		*err = -ENOMEM;
> +		return NULL;
> +	}
> +
>  	mutex_lock(&sbi->s_alloc_mutex);
>  	if (sbi->s_lvid_bh) {
>  		struct logicalVolIntegrityDesc *lvid =
> @@ -129,25 +148,6 @@ struct inode *udf_new_inode(struct inode *dir, int mode, int *err)
>  	iinfo->i_lenEAttr = 0;
>  	iinfo->i_lenAlloc = 0;
>  	iinfo->i_use = 0;
> -	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_EXTENDED_FE)) {
> -		iinfo->i_efe = 1;
> -		if (UDF_VERS_USE_EXTENDED_FE > sbi->s_udfrev)
> -			sbi->s_udfrev = UDF_VERS_USE_EXTENDED_FE;
> -		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
> -					    sizeof(struct extendedFileEntry),
> -					    GFP_KERNEL);
> -	} else {
> -		iinfo->i_efe = 0;
> -		iinfo->i_ext.i_data = kzalloc(inode->i_sb->s_blocksize -
> -					    sizeof(struct fileEntry),
> -					    GFP_KERNEL);
> -	}
> -	if (!iinfo->i_ext.i_data) {
> -		iput(inode);
> -		*err = -ENOMEM;
> -		mutex_unlock(&sbi->s_alloc_mutex);
> -		return NULL;
> -	}
>  	if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_AD_IN_ICB))
>  		iinfo->i_alloc_type = ICBTAG_FLAG_AD_IN_ICB;
>  	else if (UDF_QUERY_FLAG(inode->i_sb, UDF_FLAG_USE_SHORT_AD))
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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