Messages in this thread | | | Date | Mon, 24 Apr 2023 11:45:22 +0800 | From | Baokun Li <> | Subject | Re: [PATCH v3 3/8] ext4: use __GFP_NOFAIL if allocating extents_status cannot fail |
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On 2023/4/13 18:30, Jan Kara wrote: > On Wed 12-04-23 20:41:21, Baokun Li wrote: >> If extent status tree update fails, we have inconsistency between what is >> stored in the extent status tree and what is stored on disk. And that can >> cause even data corruption issues in some cases. >> >> For extents that cannot be dropped we use __GFP_NOFAIL to allocate memory. >> And with the above logic, the undo operation in __es_remove_extent that >> may cause inconsistency if the split extent fails is unnecessary, so we >> remove it as well. >> >> Suggested-by: Jan Kara<jack@suse.cz> >> Signed-off-by: Baokun Li<libaokun1@huawei.com> > When I was looking through this patch, I've realized there's a problem with > my plan :-|. See below... > >> static struct extent_status * >> ext4_es_alloc_extent(struct inode *inode, ext4_lblk_t lblk, ext4_lblk_t len, >> - ext4_fsblk_t pblk) >> + ext4_fsblk_t pblk, int nofail) >> { >> struct extent_status *es; >> - es = kmem_cache_alloc(ext4_es_cachep, GFP_ATOMIC); >> + gfp_t gfp_flags = GFP_ATOMIC; >> + >> + if (nofail) >> + gfp_flags |= __GFP_NOFAIL; >> + >> + es = kmem_cache_alloc(ext4_es_cachep, gfp_flags); >> if (es == NULL) >> return NULL; > I have remembered that the combination of GFP_ATOMIC and GFP_NOFAIL is > discouraged because the kernel has no sane way of refilling reserves for > atomic allocations when in atomic context. So this combination can result > in lockups.
Indeed. GFP_NOFAIL is only applicable to sleepable allocations,
GFP_ATOMIC will ignore it. I didn't notice that.
> So what I think we'll have to do is that we'll just have to return error > from __es_insert_extent() and __es_remove_extent() and in the callers we > drop the i_es_lock, allocate needed status entries (one or two depending on > the desired operation) with GFP_KERNEL | GFP_NOFAIL, get the lock again and > pass the preallocated entries into __es_insert_extent / > __es_remove_extent(). It's a bit ugly but we can at least remove those > __es_shrink() calls which are not pretty either. > > Honza
Yes, there's really no better way, thank you very much for your review! I've sent a patch for v4 as you suggested. Thanks again!
-- With Best Regards, Baokun Li .
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