On Mon, Mar 15, 2021 at 06:36:34PM +0100, Vlastimil Babka wrote: > On 3/15/21 6:32 PM, Paul E. McKenney wrote: > > On Mon, Mar 15, 2021 at 06:28:42PM +0100, Vlastimil Babka wrote: > >> On 3/15/21 6:16 PM, David Rientjes wrote: > >> > On Mon, 15 Mar 2021, Vlastimil Babka wrote: > >> > > >> >> Commit ca0cab65ea2b ("mm, slub: introduce static key for slub_debug()") > >> >> introduced a static key to optimize the case where no debugging is enabled for > >> >> any cache. The static key is enabled when slub_debug boot parameter is passed, > >> >> or CONFIG_SLUB_DEBUG_ON enabled. > >> >> > >> >> However, some caches might be created with one or more debugging flags > >> >> explicitly passed to kmem_cache_create(), and the commit missed this. Thus the > >> >> debugging functionality would not be actually performed for these caches unless > >> >> the static key gets enabled by boot param or config. > >> >> > >> >> This patch fixes it by checking for debugging flags passed to > >> >> kmem_cache_create() and enabling the static key accordingly. > >> >> > >> >> Note such explicit debugging flags should not be used outside of debugging and > >> >> testing as they will now enable the static key globally. btrfs_init_cachep() > >> >> creates a cache with SLAB_RED_ZONE but that's a mistake that's being corrected > >> >> [1]. rcu_torture_stats() creates a cache with SLAB_STORE_USER, but that is a > >> >> testing module so it's OK and will start working as intended after this patch. > >> >> > >> >> Also note that in case of backports to kernels before v5.12 that don't have > >> >> 59450bbc12be ("mm, slab, slub: stop taking cpu hotplug lock"), > >> >> static_branch_enable_cpuslocked() should be used. > >> >> > >> > > >> > Since this affects 5.9+, is the plan to propose backports to stable with > >> > static_branch_enable_cpuslocked() once this is merged? (I notice the > >> > absence of the stable tag here, which I believe is intended.) > >> > >> I was thinking about it, and since the rcutorture user is only in -next (AFAICS) > >> and btrfs user was unintended, it didn't seem to meet stable criteria to me. But > >> I won't mind if it's backported. > > > > I had better ask... Should rcutorture be doing something different? > > > > Thanx, Paul > > No, I think it's fine if a testing module such as rcutorture flips the static > key for the rest of the kernel's uptime. I only CC'd you as FYI in case you were > wondering why you can't see any alloc/free stacks in its output :) Ah, all of my recent tests have been for sufficient duration that all was well by the time that that code was invoked. But thank you for the heads up -- someone will hit this sooner or later, and I freely confess that I would have been clueless. Thanx, Paul