Le 22/04/2022 à 09:34, Michal Hocko a écrit :
On Fri 22-04-22 09:15:21, Christophe JAILLET wrote:
There is no point in doing put_device()/device_unregister() on a
device that has just been registered a few lines above. This will lead to
a double reference decrement.
This is a bit confusing. I would rephrase.
"
__add_memory_block calls both put_device and device_unregister when
storing the memory block into the xarray. This is incorrect because
xarray doesn't take an additional reference and device_unregister
already calls put_device.
"
Btw. I do not think this failure path can be triggered, or is there a
way to hit it?
I guess that this put_device()/device_unregister() is a cut'n'paste from
remove_memory_block() (i.e. unregister_memory() at the time being) which
does need it.
Fixes: 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup")
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
Other than that looks good to me. With the changelog clarified,
especially the part that evaluates whether this is a real or a
theoretical problem, feel free to add
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
I'll send a v2 with the updated changelog.
I do agree that this is certainly a theoretical issue.
Moreover, should it be triggered, I think that it would only print a
warning message about an erroneous decrement on a ref counted resource
that is already 0.
Well, it also saves 2 LoC and will look more logical to other readers
(and static checkers :) )
Thanks for the quick review for both of you.
CJ
Thanks!
---
drivers/base/memory.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 7222ff9b5e05..084d67fd55cc 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -636,10 +636,9 @@ static int __add_memory_block(struct memory_block *memory)
}
ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory,
GFP_KERNEL));
- if (ret) {
- put_device(&memory->dev);
+ if (ret)
device_unregister(&memory->dev);
- }
+
return ret;
}
--
2.32.0
