Messages in this thread | | | Subject | Re: [PATCH v2] ceph: invalidate pages when doing DIO in encrypted inodes | From | Xiubo Li <> | Date | Thu, 7 Apr 2022 09:17:40 +0800 |
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On 4/6/22 9:41 PM, Jeff Layton wrote: > On Wed, 2022-04-06 at 21:10 +0800, Xiubo Li wrote: >> On 4/6/22 7:48 PM, Jeff Layton wrote: >>> On Wed, 2022-04-06 at 12:33 +0100, Luís Henriques wrote: >>>> Xiubo Li <xiubli@redhat.com> writes: >>>> >>>>> On 4/6/22 6:57 PM, Luís Henriques wrote: >>>>>> Xiubo Li <xiubli@redhat.com> writes: >>>>>> >>>>>>> On 4/1/22 9:32 PM, Luís Henriques wrote: >>>>>>>> When doing DIO on an encrypted node, we need to invalidate the page cache in >>>>>>>> the range being written to, otherwise the cache will include invalid data. >>>>>>>> >>>>>>>> Signed-off-by: Luís Henriques <lhenriques@suse.de> >>>>>>>> --- >>>>>>>> fs/ceph/file.c | 11 ++++++++++- >>>>>>>> 1 file changed, 10 insertions(+), 1 deletion(-) >>>>>>>> >>>>>>>> Changes since v1: >>>>>>>> - Replaced truncate_inode_pages_range() by invalidate_inode_pages2_range >>>>>>>> - Call fscache_invalidate with FSCACHE_INVAL_DIO_WRITE if we're doing DIO >>>>>>>> >>>>>>>> Note: I'm not really sure this last change is required, it doesn't really >>>>>>>> affect generic/647 result, but seems to be the most correct. >>>>>>>> >>>>>>>> diff --git a/fs/ceph/file.c b/fs/ceph/file.c >>>>>>>> index 5072570c2203..b2743c342305 100644 >>>>>>>> --- a/fs/ceph/file.c >>>>>>>> +++ b/fs/ceph/file.c >>>>>>>> @@ -1605,7 +1605,7 @@ ceph_sync_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos, >>>>>>>> if (ret < 0) >>>>>>>> return ret; >>>>>>>> - ceph_fscache_invalidate(inode, false); >>>>>>>> + ceph_fscache_invalidate(inode, (iocb->ki_flags & IOCB_DIRECT)); >>>>>>>> ret = invalidate_inode_pages2_range(inode->i_mapping, >>>>>>>> pos >> PAGE_SHIFT, >>>>>>>> (pos + count - 1) >> PAGE_SHIFT); >>>>>>> The above has already invalidated the pages, why doesn't it work ? >>>>>> I suspect the reason is because later on we loop through the number of >>>>>> pages, call copy_page_from_iter() and then ceph_fscrypt_encrypt_pages(). >>>>> Checked the 'copy_page_from_iter()', it will do the kmap for the pages but will >>>>> kunmap them again later. And they shouldn't update the i_mapping if I didn't >>>>> miss something important. >>>>> >>>>> For 'ceph_fscrypt_encrypt_pages()' it will encrypt/dencrypt the context inplace, >>>>> IMO if it needs to map the page and it should also unmap it just like in >>>>> 'copy_page_from_iter()'. >>>>> >>>>> I thought it possibly be when we need to do RMW, it may will update the >>>>> i_mapping when reading contents, but I checked the code didn't find any >>>>> place is doing this. So I am wondering where tha page caches come from ? If that >>>>> page caches really from reading the contents, then we should discard it instead >>>>> of flushing it back ? >>>>> >>>>> BTW, what's the problem without this fixing ? xfstest fails ? >>>> Yes, generic/647 fails if you run it with test_dummy_encryption. And I've >>>> also checked that the RMW code was never executed in this test. >>>> >>>> But yeah I have assumed (perhaps wrongly) that the kmap/kunmap could >>>> change the inode->i_mapping. >>>> >>> No, kmap/unmap are all about high memory and 32-bit architectures. Those >>> functions are usually no-ops on 64-bit arches. >> Yeah, right. >> >> So they do nothing here. >> >>>> In my debugging this seemed to be the case >>>> for the O_DIRECT path. That's why I added this extra call here. >>>> >>> I agree with Xiubo that we really shouldn't need to invalidate multiple >>> times. >>> >>> I guess in this test, we have a DIO write racing with an mmap read >>> Probably what's happening is either that we can't invalidate the page >>> because it needs to be cleaned, or the mmap read is racing in just after >>> the invalidate occurs but before writeback. >> This sounds a possible case. >> >> >>> In any case, it might be interesting to see whether you're getting >>> -EBUSY back from the new invalidate_inode_pages2 calls with your patch. >>> >> If it's really this case maybe this should be retried some where ? >> > Possibly, or we may need to implement ->launder_folio. > > Either way, we need to understand what's happening first and then we can > figure out a solution for it.
Yeah, make sense.
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