Hi,
[please don't trim the Cc list]
On (11/02/15 21:53), Geliang Tang wrote:
> > Those things are not connected, absolutely. zram_meta_alloc() can fail
> > even on un-initialized device. In any case disksize_store() does not end
> > up changing the state of the device and reports the error back, so I don't
> > see any real value in this change. Seems that we come across this change
> > something like once a year (this patch is not the first).
>
> Thanks for your reply.
>
> zram_meta_alloc() always fails on initialized device at debugfs_create_dir():
> debugfs dir <zram0> creation failed
Aha, so you are talking about calling disksize_store() on
- already initialized device that
- uses zsmalloc with
- CONFIG_ZSMALLOC_STAT as an alacator
(zbud is not affected). that should have been mentioned in the commit message.
hm, does the patch _actually_ make it better? splitting a ->init_lock regions
is *never* a good idea. consider an un-initialized device.
CPU0 CPU1
down_read(&zram->init_lock);
if (init_done(zram))
return -EBUSY;
up_read(&zram->init_lock);
down_read(&zram->init_lock);
if (init_done(zram))
return -EBUSY;
up_read(&zram->init_lock);
meta = zram_meta_alloc();
meta = zram_meta_alloc();
comp = zcomp_create();
comp = zcomp_create();
down_write(&zram->init_lock);
zram->meta = meta;
...
up_write(&zram->init_lock);
down_write(&zram->init_lock);
zram->meta = meta;
...
up_write(&zram->init_lock);
So the above code will return a "debugfs dir <zram0> creation failed"
IFF zsmalloc with CONFIG_ZSMALLOC_STAT enabled is being used (regardless the
effort). And it will totally succeed and lead to N (depending on the number of
concurrent disksize_store() calls) pool memory and zcomp_create memory leaks
otherwise. Because of this part:
---
down_write(&zram->init_lock);
- if (init_done(zram)) {
- pr_info("Cannot change disksize for initialized device\n");
- err = -EBUSY;
- goto out_destroy_comp;
- }
-
init_waitqueue_head(&zram->io_done);
atomic_set(&zram->refcount, 1);
zram->meta = meta;
---
> zram: Error creating memory pool
>
> I think we should deal with this error.
Is it so critical? I mean it does not break the existing device; we
print the error and keep the existing device fully functional. The
error line may be a bit misleading, which is another thing and can
be solved documenting the behavior, *for example*. (I just don't
really want to complicate the code for a corner case which doesn't
even break anything).
-ss
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