On Tue, Apr 28, 2026 at 05:20:07PM +0800, Linlin Zhang wrote: > > > On 4/28/2026 7:21 AM, Benjamin Marzinski wrote: > > On Mon, Apr 27, 2026 at 01:23:27AM -0400, Benjamin Marzinski wrote: > >> On Fri, Apr 10, 2026 at 06:40:30AM -0700, Linlin Zhang wrote: > >>> From: Eric Biggers <[email protected]> > >>> + /* > >>> + * Since we've added an encryption context to the bio and > >>> + * blk-crypto-fallback may be needed to process it, it's necessary to > >>> + * use the fallback-aware bio submission code rather than > >>> + * unconditionally returning DM_MAPIO_REMAPPED. > >>> + * > >>> + * To get the correct accounting for a dm target in the case where > >>> + * __blk_crypto_submit_bio() doesn't take ownership of the bio (returns > >>> + * true), call __blk_crypto_submit_bio() directly and return > >>> + * DM_MAPIO_REMAPPED in that case, rather than relying on > >>> + * blk_crypto_submit_bio() which calls submit_bio() in that case. > >>> + */ > >>> + if (__blk_crypto_submit_bio(bio)) > >> > >> This will still double account for fallback writes (which call > >> submit_bio() on the encrypted bios, and return DM_MAPIO_SUBMITTED here). > > > > Just to clarify, I'm talking about the vmstats accounting. The IO > > originally gets accounted by submit_bio() when the bio is submitted to > > the dm device. For actual inline encryption and fallback reads, dm will > > submit the bio to the underlying device using submit_bio_noacct() to > > avoid double-counting the IO. > > > > For fallback writes, __blk_crypto_submit_bio() will submit the encrypted > > bios to the underlying device with submit_bio(). This adds the IO > > sectors again, even though it's the same IO, only encrypted now. > > > Right, thanks for calling this out. > > For fallback writes, the IO is still double-counted. Given that this only > affects IO accounting in the blk-crypto fallback write slow-path and not > correctness, I think this is an acceptable tradeoff, and we can leave a > TODO to revisit the accounting once a better solution exists. > > Add the bellow to the annotate. > > /* > * TODO: blk-crypto fallback write slow-path currently double-accounts > * IO in vmstat, as encrypted bios are submitted via submit_bio(). > * This does not affect data correctness. Consider fixing this if > * a cleaner accounting model for derived bios is introduced. > */ > > Do you agree?
You could add an extra argument, for instance "bool need_acct", to __blk_crypto_submit_bio(), and plumb it through to __blk_crypto_fallback_encrypt_bio(), where it could be used to choose between calling submit_bio() and and submit_bio_noacct(). We could even add a flag to cloned bios for stacked devices, that could be checked in submit_bio(), so we didn't need to have submit_bio_noacct(). But this is a pretty niche case with other solutions, so I'm not sure if it warrants adding more checks to submit_bio(). I do agree that people probably aren't using dm-inlinecrypt for devices where they don't actually have inline encryption capabilities, so it's not a major issue. What to you think, Mikulas? -Ben > > > > -Ben > > > >> > >> -Ben > >> > >>> + return DM_MAPIO_REMAPPED; > >>> + return DM_MAPIO_SUBMITTED; > >>> +} > >> > >
