Re: [f2fs-dev] [PATCH v2] f2fs: don't return vmalloc() memory from f2fs_kmalloc()

[Eric Biggers <ebiggers@kernel.org>]

On Tue, Jun 09, 2020 at 09:36:50AM +0800, Chao Yu wrote:
> On 2020/6/5 12:57, Eric Biggers wrote:
> > From: Eric Biggers <ebiggers@google.com>
> > 
> > kmalloc() returns kmalloc'ed memory, and kvmalloc() returns either
> > kmalloc'ed or vmalloc'ed memory.  But the f2fs wrappers, f2fs_kmalloc()
> > and f2fs_kvmalloc(), both return both kinds of memory.
> > 
> > It's redundant to have two functions that do the same thing, and also
> > breaking the standard naming convention is causing bugs since people
> > assume it's safe to kfree() memory allocated by f2fs_kmalloc().  See
> > e.g. the various allocations in fs/f2fs/compress.c.
> > 
> > Fix this by making f2fs_kmalloc() just use kmalloc().  And to avoid
> > re-introducing the allocation failures that the vmalloc fallback was
> > intended to fix, convert the largest allocations to use f2fs_kvmalloc().
> > 
> > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > ---
> > 
> > v2: also use f2fs_kvzalloc() in init_blkz_info()
> > 
> >  fs/f2fs/checkpoint.c | 4 ++--
> >  fs/f2fs/f2fs.h       | 8 +-------
> >  fs/f2fs/node.c       | 8 ++++----
> >  fs/f2fs/super.c      | 2 +-
> >  4 files changed, 8 insertions(+), 14 deletions(-)
> > 
> > diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
> > index 3dc3ac6fe14324..23606493025165 100644
> > --- a/fs/f2fs/checkpoint.c
> > +++ b/fs/f2fs/checkpoint.c
> > @@ -895,8 +895,8 @@ int f2fs_get_valid_checkpoint(struct f2fs_sb_info *sbi)
> >  	int i;
> >  	int err;
> >  
> > -	sbi->ckpt = f2fs_kzalloc(sbi, array_size(blk_size, cp_blks),
> > -				 GFP_KERNEL);
> > +	sbi->ckpt = f2fs_kvzalloc(sbi, array_size(blk_size, cp_blks),
> > +				  GFP_KERNEL);
> >  	if (!sbi->ckpt)
> >  		return -ENOMEM;
> >  	/*
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 50e6cdf20b7331..c812fb8e2d9c7a 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -2998,18 +2998,12 @@ static inline bool f2fs_may_extent_tree(struct inode *inode)
> >  static inline void *f2fs_kmalloc(struct f2fs_sb_info *sbi,
> >  					size_t size, gfp_t flags)
> >  {
> > -	void *ret;
> > -
> >  	if (time_to_inject(sbi, FAULT_KMALLOC)) {
> >  		f2fs_show_injection_info(sbi, FAULT_KMALLOC);
> >  		return NULL;
> >  	}
> >  
> > -	ret = kmalloc(size, flags);
> > -	if (ret)
> > -		return ret;
> > -
> > -	return kvmalloc(size, flags);
> > +	return kmalloc(size, flags);
> 
> Then could we revert to use kfree instead of kvfree if memory was allocated
> from f2fs_kmalloc()? though there is actual problem w/o reverting.
> 

Yes, I think we should prefer kfree() when the memory was allocated with
f2fs_kmalloc().  It's not critical though, since kvfree() works on kmalloc'ed
memory.  So it should be a separate patch later.

- Eric


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