On Mon, May 1, 2017 at 8:43 AM, Dan Williams <dan.j.willi...@intel.com> wrote: > On Mon, May 1, 2017 at 8:34 AM, Kani, Toshimitsu <toshi.k...@hpe.com> wrote: >> On Sun, 2017-04-30 at 05:39 -0700, Dan Williams wrote: >>> Toshi noticed that the new support for a region-level badblocks >>> missed the case where errors are cleared due to BTT I/O. >>> >>> An initial attempt to fix this ran into a "sleeping while atomic" >>> warning due to taking the nvdimm_bus_lock() in the BTT I/O path to >>> satisfy the locking requirements of __nvdimm_bus_badblocks_clear(). >>> However, that lock is not needed since we are not acting any data >>> that is subject to change due to a change of state of the bus / >>> region. The badblocks instance has its own internal lock to handle >>> mutations of the error list. >>> >>> So, to make it clear that we are just acting on region devices and >>> don't need the lock rename __nvdimm_bus_badblocks_clear() to >>> nvdimm_clear_badblocks_regions(). Eliminate the lock and consolidate >>> all routines in drivers/nvdimm/bus.c. Also, make some cleanups to >>> remove unnecessary casts, make the calling convention of >>> nvdimm_clear_badblocks_regions() clearer by replacing struct resource >>> with the minimal struct clear_badblocks_context, and use the >>> DEVICE_ATTR macro. >> >> Hi Dan, >> >> I was testing the change with CONFIG_DEBUG_ATOMIC_SLEEP set this time, >> and hit the following BUG with BTT. This is a separate issue (not >> introduced by this patch), but it shows that we have an issue with the >> DSM call path as well. > > Ah, great find, thanks! We don't see this in the unit tests because > the nfit_test infrastructure takes no sleeping actions in its > simulated DSM path. Outside of converting btt to use sleeping locks > I'm not sure I see a path forward. I wonder how bad the performance > impact of that would be? Perhaps with opportunistic spinning it won't > be so bad, but I don't see another choice.
It's worse than that. Part of the performance optimization of BTT I/O was to avoid locking altogether when we could rely on a BTT lane percpu, so that would also need to be removed.
