linux-kernel - Re: [PATCH 1/2] ext4: Check stripe size compatibility on remount as well

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Message-ID: <ZsQ4IA84NCRcVJg5@li-bb2b2a4c-3307-11b2-a85c-8fa5c3a69313.ibm.com>
Date: Tue, 20 Aug 2024 12:00:56 +0530
From: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>,
        Ritesh Harjani <ritesh.list@...il.com>, linux-kernel@...r.kernel.org,
        syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
Subject: Re: [PATCH 1/2] ext4: Check stripe size compatibility on remount as
 well

On Mon, Aug 19, 2024 at 08:31:26PM +0800, Kemeng Shi wrote:
> 
> 
> on 8/16/2024 3:57 PM, Ojaswin Mujoo wrote:
> > We disable stripe size in __ext4_fill_super if it is not a multiple of
> > the cluster ratio however this check is missed when trying to remount.
> > This can leave us with cases where stripe < cluster_ratio after
> > remount:set making EXT4_B2C(sbi->s_stripe) become 0 that can cause some
> > unforeseen bugs like divide by 0.
> > 
> > Fix that by adding the check in remount path as well.
> > 
> > Additionally, change the users of EXT4_B2C(sbi->s_stripe) to
> > EXT4_NUM_B2C() so that if we ever accidentally hit this again, we can
> > avoid the value becoming 0. This should not change existing functionality.
> It's better to mention this change is in following patch or simply remove
> it from this patch.

Oh yes you are right, I accidentally left it here. I'll fix it.
> 
> Other than that, looks good to me. Feel free to add:
> 
> Reviewed-by: Kemeng Shi <shikemeng@...weicloud.com>

Thanks for the review!

Regards,
Ojaswin
> > 
> > Reported-by: syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
> > Tested-by: syzbot+1ad8bac5af24d01e2cbd@...kaller.appspotmail.com
> > Fixes: c3defd99d58c ("ext4: treat stripe in block unit")
> > Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
> > ---
> >  fs/ext4/super.c | 29 ++++++++++++++++++++++-------
> >  1 file changed, 22 insertions(+), 7 deletions(-)
> > 
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index e72145c4ae5a..9d495d78d262 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -5165,6 +5165,18 @@ static int ext4_block_group_meta_init(struct super_block *sb, int silent)
> >  	return 0;
> >  }
> >  
> > +/*
> > + * It's hard to get stripe aligned blocks if stripe is not aligned with
> > + * cluster, just disable stripe and alert user to simpfy code and avoid
> > + * stripe aligned allocation which will rarely successes.
> > + */
> > +static bool ext4_is_stripe_incompatible(struct super_block *sb, unsigned long stripe)
> > +{
> > +	struct ext4_sb_info *sbi = EXT4_SB(sb);
> > +	return (stripe > 0 && sbi->s_cluster_ratio > 1 &&
> > +		stripe % sbi->s_cluster_ratio != 0);
> > +}
> > +
> >  static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
> >  {
> >  	struct ext4_super_block *es = NULL;
> > @@ -5272,13 +5284,7 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
> >  		goto failed_mount3;
> >  
> >  	sbi->s_stripe = ext4_get_stripe_size(sbi);
> > -	/*
> > -	 * It's hard to get stripe aligned blocks if stripe is not aligned with
> > -	 * cluster, just disable stripe and alert user to simpfy code and avoid
> > -	 * stripe aligned allocation which will rarely successes.
> > -	 */
> > -	if (sbi->s_stripe > 0 && sbi->s_cluster_ratio > 1 &&
> > -	    sbi->s_stripe % sbi->s_cluster_ratio != 0) {
> > +	if (ext4_is_stripe_incompatible(sb, sbi->s_stripe)) {
> >  		ext4_msg(sb, KERN_WARNING,
> >  			 "stripe (%lu) is not aligned with cluster size (%u), "
> >  			 "stripe is disabled",
> > @@ -6441,6 +6447,15 @@ static int __ext4_remount(struct fs_context *fc, struct super_block *sb)
> >  
> >  	}
> >  
> > +	if ((ctx->spec & EXT4_SPEC_s_stripe) &&
> > +	    ext4_is_stripe_incompatible(sb, ctx->s_stripe)) {
> > +		ext4_msg(sb, KERN_WARNING,
> > +			 "stripe (%lu) is not aligned with cluster size (%u), "
> > +			 "stripe is disabled",
> > +			 ctx->s_stripe, sbi->s_cluster_ratio);
> > +		ctx->s_stripe = 0;
> > +	}
> > +
> >  	/*
> >  	 * Changing the DIOREAD_NOLOCK or DELALLOC mount options may cause
> >  	 * two calls to ext4_should_dioread_nolock() to return inconsistent
> > 
>