DECLARE_WAIT_QUEUE_HEAD_ONSTACK triggers -Wuninitialized

[nathanchance]

mm/shmem.c:2719:35: warning: variable 'shmem_falloc_waitq' is uninitialized when used within its own initialization [-Wuninitialized]
                DECLARE_WAIT_QUEUE_HEAD_ONSTACK(shmem_falloc_waitq);
                                                ^~~~~~~~~~~~~~~~~~
include/linux/wait.h:74:63: note: expanded from macro 'DECLARE_WAIT_QUEUE_HEAD_ONSTACK'
        struct wait_queue_head name = __WAIT_QUEUE_HEAD_INIT_ONSTACK(name)
                               ~~~~                                  ^~~~
include/linux/wait.h:72:33: note: expanded from macro '__WAIT_QUEUE_HEAD_INIT_ONSTACK'
        ({ init_waitqueue_head(&name); name; })
                                       ^~~~
1 warning generated.

Arnd has a proposed fix that has not been sent out yet: https://lore.kernel.org/lkml/CAK8P3a20t1f6Fmjd7HcGVSXCxx9SP2q7_WpZyj16MgnJe8m8zQ@mail.gmail.com/

[nickdesaulniers]

Multiple instances of this:

fs/proc/base.c:1876:35: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/proc/proc_sysctl.c:701:35: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/namei.c:1646:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/namei.c:3136:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/afs/dir_silly.c:205:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/cifs/readdir.c:83:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
drivers/bluetooth/bluecard_cs.c:282:36: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/fuse/readdir.c:161:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/nfs/dir.c:451:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]
fs/nfs/dir.c:1573:34: warning: variable 'wq' is uninitialized when used within its own initialization [-Wuninitialized]net/nfc/hci/command.c:59:34: warning: variable 'ew_wq' is uninitialized when used within its own initialization [-Wuninitialized]
net/nfc/hci/llc_shdlc.c:687:34: warning: variable 'connect_wq' is uninitialized when used within its own initialization [-Wuninitialized]
...

Reported-by: kernelci.org bot bot@kernelci.org
arm64 linux-next

[nathanchance]

Patch submitted: https://lore.kernel.org/lkml/20190703081119.209976-1-arnd@arndb.de/

[nathanchance]

Andrew Morton pushed back a bit while still tentatively picking up the patch:

https://lore.kernel.org/lkml/20190711174949.dc74310efd1fd3c8bd4ea276@linux-foundation.org/

https://www.ozlabs.org/~akpm/mmotm/broken-out/waitqueue-fix-clang-wuninitialized-warnings.patch

creduce spits out:

struct a {
} __init_waitqueue_head(struct a *, int);
b(void) {
  struct a c = ({
    __init_waitqueue_head((&c), b);
    c;
  });
}

With the following interestingness script:

#!/bin/bash

grep -F "__init_waitqueue_head((" shmem.i || exit 1

gcc -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mpreferred-stack-boundary=3 -mskip-rax-setup -mtune=generic -mno-red-zone -mcmodel=kernel -Wno-sign-compare -fno-asynchronous-unwind-tables -mindirect-branch=thunk-extern -mindirect-branch-register -fno-jump-tables -fno-delete-null-pointer-checks -Wno-frame-address -Wno-format-truncation -Wno-format-overflow -Wno-address-of-packed-member -O2 --param=allow-store-data-races=0 -Wframe-larger-than=2048 -fstack-protector-strong -Wno-unused-but-set-variable -Wno-unused-const-variable -fomit-frame-pointer -fno-var-tracking-assignments -Wdeclaration-after-statement -Wimplicit-fallthrough=3 -Wvla -Wno-pointer-sign -Wno-stringop-truncation -fno-strict-overflow -fno-merge-all-constants -fmerge-constants -fno-stack-check -fconserve-stack -Werror=date-time -Werror=incompatible-pointer-types -Werror=designated-init -fmacro-prefix-map=./= -Wno-packed-not-aligned -c -o shmem.o shmem.i || exit 1

/home/nathan/cbl/usr/bin/clang -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE -Werror=implicit-function-declaration -Werror=implicit-int -Wno-format-security -std=gnu89 -no-integrated-as -Werror=unknown-warning-option -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -mno-80387 -mstack-alignment=8 -mtune=generic -mno-red-zone -mcmodel=kernel -Wno-sign-compare -fno-asynchronous-unwind-tables -mretpoline-external-thunk -fno-delete-null-pointer-checks -Wno-address-of-packed-member -O2 -Wframe-larger-than=2048 -fstack-protector-strong -Wno-format-invalid-specifier -Wno-gnu -Wno-tautological-compare -mno-global-merge -Wno-unused-const-variable -fomit-frame-pointer -ftrivial-auto-var-init=pattern -Wdeclaration-after-statement -Wvla -Wno-pointer-sign -fno-strict-overflow -fno-merge-all-constants -fno-stack-check -Werror=date-time -Werror=incompatible-pointer-types -Wno-initializer-overrides -Wno-format -Wno-sign-compare -Wno-format-zero-length -c -o shmem.o shmem.i |& grep -F "is uninitialized when used within its own initialization [-Wuninitialized]"

I cleaned it up as I don't think the second parameter of __init_waitqueue_head is entirely necessary: https://godbolt.org/z/l0Z9UA

[nickdesaulniers]

https://llvm.org/pr42604 (just seeing your creduce case @nathanchance now, sorry. Looks like the same thing I wrote up in the BR).

[nathanchance]

No worries, I think yours makes it clearer what is going on here :)

[nickdesaulniers]

WIP: https://reviews.llvm.org/D64678

[nickdesaulniers]

https://reviews.llvm.org/rL367134

[nickdesaulniers]

The Clang-9 release manager Hans picked this up for clang-9: r367150