block: Disable -Walign-mismatch for blk-mq.c
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Message ID 20210408194458.501617-1-nathan@kernel.org
State New, archived
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  • block: Disable -Walign-mismatch for blk-mq.c
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Commit Message

Nathan Chancellor April 8, 2021, 7:44 p.m. UTC
LLVM 13 adds a new warning, -Walign-mismatch, which has an instance in
blk_mq_complete_send_ipi():

block/blk-mq.c:630:39: warning: passing 8-byte aligned argument to
32-byte aligned parameter 2 of 'smp_call_function_single_async' may
result in an unaligned pointer access [-Walign-mismatch]
                smp_call_function_single_async(cpu, &rq->csd);
                                                    ^
1 warning generated.

This is expected after commit 4ccafe032005 ("block: unalign
call_single_data in struct request"), which purposefully unaligned the
structure to save space. Given that there is no real alignment
requirement and there have been no reports of issues since that change,
it should be safe to disable the warning for this one translation unit.

Link: https://github.com/ClangBuiltLinux/linux/issues/1328
Link: https://lore.kernel.org/r/20210310182307.zzcbi5w5jrmveld4@archlinux-ax161/
Link: https://lore.kernel.org/r/20210330230249.709221-1-jiancai@google.com/
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
 block/Makefile | 1 +
 1 file changed, 1 insertion(+)


base-commit: e49d033bddf5b565044e2abe4241353959bc9120

Comments

Guenter Roeck April 8, 2021, 7:52 p.m. UTC | #1
On 4/8/21 12:44 PM, Nathan Chancellor wrote:
> LLVM 13 adds a new warning, -Walign-mismatch, which has an instance in
> blk_mq_complete_send_ipi():
> 
> block/blk-mq.c:630:39: warning: passing 8-byte aligned argument to
> 32-byte aligned parameter 2 of 'smp_call_function_single_async' may
> result in an unaligned pointer access [-Walign-mismatch]
>                 smp_call_function_single_async(cpu, &rq->csd);
>                                                     ^
> 1 warning generated.
> 
> This is expected after commit 4ccafe032005 ("block: unalign
> call_single_data in struct request"), which purposefully unaligned the
> structure to save space. Given that there is no real alignment
> requirement and there have been no reports of issues since that change,
> it should be safe to disable the warning for this one translation unit.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/1328
> Link: https://lore.kernel.org/r/20210310182307.zzcbi5w5jrmveld4@archlinux-ax161/
> Link: https://lore.kernel.org/r/20210330230249.709221-1-jiancai@google.com/
> Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Reviewed-by: Guenter Roeck <linux@roeck-us.net>

> ---
>  block/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/block/Makefile b/block/Makefile
> index 8d841f5f986f..d69ac0bd8e61 100644
> --- a/block/Makefile
> +++ b/block/Makefile
> @@ -10,6 +10,7 @@ obj-$(CONFIG_BLOCK) := bio.o elevator.o blk-core.o blk-sysfs.o \
>  			blk-mq-sysfs.o blk-mq-cpumap.o blk-mq-sched.o ioctl.o \
>  			genhd.o ioprio.o badblocks.o partitions/ blk-rq-qos.o
>  
> +CFLAGS_blk-mq.o := $(call cc-disable-warning, align-mismatch)
>  obj-$(CONFIG_BOUNCE)		+= bounce.o
>  obj-$(CONFIG_BLK_SCSI_REQUEST)	+= scsi_ioctl.o
>  obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o
> 
> base-commit: e49d033bddf5b565044e2abe4241353959bc9120
>

Patch
diff mbox series

diff --git a/block/Makefile b/block/Makefile
index 8d841f5f986f..d69ac0bd8e61 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -10,6 +10,7 @@  obj-$(CONFIG_BLOCK) := bio.o elevator.o blk-core.o blk-sysfs.o \
 			blk-mq-sysfs.o blk-mq-cpumap.o blk-mq-sched.o ioctl.o \
 			genhd.o ioprio.o badblocks.o partitions/ blk-rq-qos.o
 
+CFLAGS_blk-mq.o := $(call cc-disable-warning, align-mismatch)
 obj-$(CONFIG_BOUNCE)		+= bounce.o
 obj-$(CONFIG_BLK_SCSI_REQUEST)	+= scsi_ioctl.o
 obj-$(CONFIG_BLK_DEV_BSG)	+= bsg.o