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charset=us-ascii Content-Disposition: inline In-Reply-To: <20200420182211.exrzkszefraeylv2@ca-dmjordan1.us.oracle.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Apr 20, 2020 at 02:22:11PM -0400, Daniel Jordan wrote: > On Tue, Apr 14, 2020 at 05:43:50PM -0700, Michel Lespinasse wrote: > > diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c > > index 11d41f0c7005..998968659892 100644 > > --- a/kernel/bpf/stackmap.c > > +++ b/kernel/bpf/stackmap.c > > @@ -317,7 +316,7 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, > > * with build_id. > > */ > > if (!user || !current || !current->mm || irq_work_busy || > > - mmap_read_trylock(current->mm) == 0) { > > + !mmap_read_trylock_non_owner(current->mm)) { > > /* cannot access current->mm, fall back to ips */ > > for (i = 0; i < trace_nr; i++) { > > id_offs[i].status = BPF_STACK_BUILD_ID_IP; > > @@ -342,16 +341,10 @@ static void stack_map_get_build_id_offset(struct bpf_stack_build_id *id_offs, > > } > > > > if (!work) { > > - mmap_read_unlock(current->mm); > > + mmap_read_unlock_non_owner(current->mm); > > These 'non_owner' calls are not intuitive because current _is the owner, so the > v3 version seems better, even if it adds a special wrapper for rwsem_release. > > Though it makes some sense if you think, "we're consistently using the > non_owner APIs because there's a legitimate use somewhere else," so I'm fine > either way. I'm not really a big fan of v3 nor v4. What I'd like to see is a 'transfer of ownership' API. This could be to a different task, IRQ work, RCU, softirq, timer, ... That would let us track locking dependencies across complex flows, eg this wouldn't be warned about right now: rcu_work(): lock(C) kfree(B) unlock(A) unlock(C) thread 1: lock(A) call_rcu(B) thread 2: lock(C) synchronize_rcu() unlock(C) but if we had an API that transferred ownership of A to RCU, then we'd see the C->RCU->A->C cycle. This is perhaps a bit much work to require of Laurent in order to get this patchset merged, but something to think about.