Messages in this thread | | | From | Alexey Brodkin <> | Subject | Re: [RESEND PATCH v2] devres: Really align data field to unsigned long long | Date | Mon, 9 Jul 2018 10:23:58 +0000 |
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Hi David,
On Mon, 2018-07-09 at 10:18 +0000, David Laight wrote: > From: Alexey Brodkin > > Sent: 09 July 2018 11:00 > > ... > > That's a good idea indeed but it doesn't solve the problem with > > struct devres_node. Consider the following snippet: > > -------------------------------->8------------------------------- > > struct mystruct { > > atomic64_t myvar; > > } > > > > struct mystruct *p; > > p = devm_kzalloc(dev, sizeof(*p), GFP_KERNEL); > > -------------------------------->8------------------------------- > > > > Here myvar address will match address of "data" member of struct devres_node. > > So if "data" is has offset of 12 bytes from the beginning of a page then > > myvar won't be 64-bit aligned regardless of myvar's attribute, right? > > ... > > > > - unsigned long long data[]; /* guarantee ull alignment */ > > Ahh, that line should be: > u8 data[] __aligned(8); /* Guarantee 64bit alignment */
And that pretty much what I suggested in my initial patch :)
For the record x86 has exactly the same atomic64_t as you suggested, see https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/atomic64_32.h#L13: ---------------------->8------------------ typedef struct { u64 __aligned(8) counter; } atomic64_t; ---------------------->8------------------
-Alexey | |