On Wed 27-03-19 07:34:32, Qian Cai wrote: > On 3/27/19 4:44 AM, Michal Hocko wrote: > >> diff --git a/mm/kmemleak.c b/mm/kmemleak.c > >> index a2d894d3de07..7f4545ab1f84 100644 > >> --- a/mm/kmemleak.c > >> +++ b/mm/kmemleak.c > >> @@ -580,7 +580,16 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size, > >> struct rb_node **link, *rb_parent; > >> unsigned long untagged_ptr; > >> > >> - object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp)); > >> + /* > >> + * The tracked memory was allocated successful, if the kmemleak object > >> + * failed to allocate for some reasons, it ends up with the whole > >> + * kmemleak disabled, so try it harder. > >> + */ > >> + gfp = (in_atomic() || irqs_disabled()) ? > >> + gfp_kmemleak_mask(gfp) | GFP_ATOMIC : > >> + gfp_kmemleak_mask(gfp) | __GFP_DIRECT_RECLAIM; > > > > > > The comment for in_atomic says: > > * Are we running in atomic context? WARNING: this macro cannot > > * always detect atomic context; in particular, it cannot know about > > * held spinlocks in non-preemptible kernels. Thus it should not be > > * used in the general case to determine whether sleeping is possible. > > * Do not use in_atomic() in driver code. > > That is why it needs both in_atomic() and irqs_disabled(), so irqs_disabled() > can detect kernel functions held spinlocks even in non-preemptible kernels. > > According to [1], > > "This [2] is useful if you know that the data in question is only ever > manipulated from a "process context", ie no interrupts involved." > > Since kmemleak only deal with kernel context, if a spinlock was held, it always > has local interrupt disabled. What? Normal spin lock implementation doesn't disable interrupts. So either I misunderstand what you are saying or you seem to be confused. the thing is that in_atomic relies on preempt_count to work properly and if you have CONFIG_PREEMPT_COUNT=n then you simply never know whether preemption is disabled so you do not know that a spin_lock is held. irqs_disabled on the other hand checks whether arch specific flag for IRQs handling is set (or cleared). So you would only catch irq safe spin locks with the above check. > ftrace is in the same boat where this commit was merged a while back that has > the same check. > > ef99b88b16be > tracing: Handle ftrace_dump() atomic context in graph_trace_open() > > [1] https://www.kernel.org/doc/Documentation/locking/spinlocks.txt > [2] > spin_lock(&lock); > ... > spin_unlock(&lock); -- Michal Hocko SUSE Labs
