> On Jul 12, 2023, at 10:02 PM, Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx> wrote: > > > >> On 2023/7/13 08:32, Joel Fernandes wrote: >> On Wed, Jul 12, 2023 at 02:20:56PM -0700, Sandeep Dhavale wrote: >> [..] >>>> As such this patch looks correct to me, one thing I noticed is that >>>> you can check rcu_is_watching() like the lockdep-enabled code does. >>>> That will tell you also if a reader-section is possible because in >>>> extended-quiescent-states, RCU readers should be non-existent or >>>> that's a bug. >>>> >>> Please correct me if I am wrong, reading from the comment in >>> kernel/rcu/update.c rcu_read_lock_held_common() >>> .. >>> * The reason for this is that RCU ignores CPUs that are >>> * in such a section, considering these as in extended quiescent state, >>> * so such a CPU is effectively never in an RCU read-side critical section >>> * regardless of what RCU primitives it invokes. >>> >>> It seems rcu will treat this as lock not held rather than a fact that >>> lock is not held. Is my understanding correct? >> If RCU treats it as a lock not held, that is a fact for RCU ;-). Maybe you >> mean it is not a fact for erofs? > > I'm not sure if I get what you mean, EROFS doesn't take any RCU read lock We are discussing the case 3 you mentioned below. > here: > > z_erofs_decompressqueue_endio() is actually a "bio->bi_end_io", previously > which can be called under two scenarios: > > 1) under softirq context, which is actually part of device I/O compleltion; > > 2) under threaded context, like what dm-verity or likewise calls. > > But EROFS needs to decompress in a threaded context anyway, so we trigger > a workqueue to resolve the case 1). > > > Recently, someone reported there could be some case 3) [I think it was > introduced recently but I have no time to dig into it]: > > case 3: under RCU read lock context, which is shown by this: > https://lore.kernel.org/r/4a8254eb-ac39-1e19-3d82-417d3a7b9f94@xxxxxxxxxxxxxxxxx/T/#u > > and such RCU read lock is taken in __blk_mq_run_dispatch_ops(). > > But as the commit shown, we only need to trigger a workqueue for case 1) > and 3) due to performance reasons. > > Hopefully I show it more clear. Makes sense. Thanks, - Joel > > Thanks, > Gao Xiang
