Re: [PATCH RFC v4 40/42] kmsan: ext4: skip block merging logic in ext4_mpage_readpages for KMSAN

From: Alexander Potapenko <glider@google.com>
To: Eric Biggers <ebiggers@google.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
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	Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH RFC v4 40/42] kmsan: ext4: skip block merging logic in ext4_mpage_readpages for KMSAN
Date: Wed, 8 Jan 2020 17:14:05 +0100	[thread overview]
Message-ID: <CAG_fn=XxPhbHNzq0t_mz30UzRYDc_oxLkqF1haA=+KXWPw5LRQ@mail.gmail.com> (raw)
In-Reply-To: <20191220191840.GA11160@google.com>

> Why is ext4 special here?  Wouldn't other filesystems need this too?
ext4 isn't special, it's just the FS we're using on syzbot.
> Is it possible the problem is the page merging logic in bio_add_page()?
> Maybe we need something like:
>
> diff --git a/block/bio.c b/block/bio.c
> index a5d75f6bf4c7e..9449a1e571ee7 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -646,6 +646,8 @@ static inline bool page_is_mergeable(const struct bio_vec *bv,
>         *same_page = ((vec_end_addr & PAGE_MASK) == page_addr);
>         if (!*same_page && pfn_to_page(PFN_DOWN(vec_end_addr)) + 1 != page)
>                 return false;
> +       if (!*same_page && IS_ENABLED(CONFIG_KMSAN))
> +               return false;
>         return true;
>  }
>

This one appears to work, thanks!
I'll pick it for v5.

-- 
Alexander Potapenko
Software Engineer

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