On Mon, Jan 22, 2024 at 07:04:20AM -0800, Greg Kroah-Hartman wrote:
On Fri, Jan 19, 2024 at 05:27:18PM +0000, Carlos Llamas wrote:
On Fri, Jan 19, 2024 at 06:49:00AM +0100, Greg Kroah-Hartman wrote:
On Thu, Jan 18, 2024 at 07:33:48PM +0000, Carlos Llamas wrote:
On Fri, Dec 01, 2023 at 05:21:34PM +0000, Carlos Llamas wrote:
Each transaction is associated with a 'struct binder_buffer' that stores the metadata about its buffer area. Since commit 74310e06be4d ("android: binder: Move buffer out of area shared with user space") this struct is no longer embedded within the buffer itself but is instead allocated on the heap to prevent userspace access to this driver-exclusive info.
Unfortunately, the space of this struct is still being accounted for in the total buffer size calculation, specifically for async transactions. This results in an additional 104 bytes added to every async buffer request, and this area is never used.
This wasted space can be substantial. If we consider the maximum mmap buffer space of SZ_4M, the driver will reserve half of it for async transactions, or 0x200000. This area should, in theory, accommodate up to 262,144 buffers of the minimum 8-byte size. However, after adding the extra 'sizeof(struct binder_buffer)', the total number of buffers drops to only 18,724, which is a sad 7.14% of the actual capacity.
This patch fixes the buffer size calculation to enable the utilization of the entire async buffer space. This is expected to reduce the number of -ENOSPC errors that are seen on the field.
Fixes: 74310e06be4d ("android: binder: Move buffer out of area shared with user space") Signed-off-by: Carlos Llamas cmllamas@google.com
Sorry, I forgot to Cc: stable@vger.kernel.org.
<formletter>
This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
</formletter>
Oops, here is the complete info:
Commit ID: c6d05e0762ab276102246d24affd1e116a46aa0c Subject: "binder: fix unused alloc->free_async_space" Reason: Fixes an incorrect calculation of available space. Versions: v4.19+
Note this patch will also have trivial conflicts in v4.19 and v5.4 kernels as commit 261e7818f06e is missing there. Please let me know and I can send the corresponding patches separately.
It doesn't even apply to 6.7.y either, so we need backports for all affected trees, thanks.
Now I got it to apply, but we need backports for 5.4.y and 4.19.y, thanks.
greg k-h