Re: [PATCH] ext4: Do not destroy ext4_groupinfo_caches if ext4_mb_init() fails

[Andrey Tsyvarev]

12.05.2014 19:08, LukÃÅ Czerner ÐÐÑÐÑ:
> On Mon, 12 May 2014, Andrey Tsyvarev wrote:
>
> > Date: Mon, 12 May 2014 12:23:59 +0400
> > From: Andrey Tsyvarev<tsyvarev@xxxxxxxxx>
> > To: Theodore Ts'o<tytso@xxxxxxx>
> > Cc: Andrey Tsyvarev<tsyvarev@xxxxxxxxx>,
> >      Andreas Dilger<adilger.kernel@xxxxxxxxx>,linux-ext4@xxxxxxxxxxxxxxx,
> >      linux-kernel@xxxxxxxxxxxxxxx, Alexey Khoroshilov<khoroshilov@xxxxxxxxx>
> > Subject: [PATCH] ext4: Do not destroy ext4_groupinfo_caches if ext4_mb_init()
> >      fails
> >
> > Caches from 'ext4_groupinfo_caches' may be in use by other mounts, which have already existed.
> > So, it is incorrect to destroy them when newly requested mount fails.
> >
> > Found by Linux File System Verification project (linuxtesting.org).
> Makes sense, thanks! Can you please share the test case which
> triggered this ? It might be worth including in xfstests.

Actually it was triggered by xfstests themselves but run with fault simulation.
The method of fault simulation is under development/evaluation now, we expect to publish a paper describing it in the near future.

BUG_ON() in get_groupinfo_cache() was firstly triggered by test generic/003, but actually it could be any other test, which uses a scratch device: xftests itself requires test device(TEST_DEV) mounted, so a fault simulated while mount scratch device causes the problem described.


> Reviewed-by: Lukas Czerner<lczerner@xxxxxxxxxx>
>
> > Signed-off-by: Andrey Tsyvarev<tsyvarev@xxxxxxxxx>
> > ---
> >   fs/ext4/mballoc.c | 4 +---
> >   1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> > index 04a5c75..becea1d 100644
> > --- a/fs/ext4/mballoc.c
> > +++ b/fs/ext4/mballoc.c
> > @@ -2607,7 +2607,7 @@ int ext4_mb_init(struct super_block *sb)
> >   	sbi->s_locality_groups = alloc_percpu(struct ext4_locality_group);
> >   	if (sbi->s_locality_groups == NULL) {
> >   		ret = -ENOMEM;
> > -		goto out_free_groupinfo_slab;
> > +		goto out;
> >   	}
> >   	for_each_possible_cpu(i) {
> >   		struct ext4_locality_group *lg;
> > @@ -2632,8 +2632,6 @@ int ext4_mb_init(struct super_block *sb)
> >   out_free_locality_groups:
> >   	free_percpu(sbi->s_locality_groups);
> >   	sbi->s_locality_groups = NULL;
> > -out_free_groupinfo_slab:
> > -	ext4_groupinfo_destroy_slabs();
> >   out:
> >   	kfree(sbi->s_mb_offsets);
> >   	sbi->s_mb_offsets = NULL;

--
Andrey Tsyvarev
Linux Verification Center, ISPRAS

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