Hi,
I did these a while back and forget. Rebased to 5.0-rc1.
Please consider applying.
Thx,
-Vineet
Vineet Gupta (3):
coredump: Replace opencoded set_mask_bits()
fs: inode_set_flags() replace opencoded set_mask_bits()
bitops.h: set_mask_bits() to return old value
fs/exec.c | 7 +------
fs/inode.c | 8 +-------
include/linux/bitops.h | 2 +-
3 files changed, 3 insertions(+), 14 deletions(-)
--
2.7.4
It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
introduced the set_mask_bits API, but somehow missed not using it in
ext4 in the end
Also, set_mask_bits is used in fs quite a bit and we can possibly come up
with a generic llsc based implementation (w/o the cmpxchg loop)
Cc: Alexander Viro <[email protected]>
Cc: Theodore Ts'o <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Vineet Gupta <[email protected]>
---
fs/inode.c | 8 +-------
1 file changed, 1 insertion(+), 7 deletions(-)
diff --git a/fs/inode.c b/fs/inode.c
index 0cd47fe0dbe5..799b0c4beda8 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2096,14 +2096,8 @@ EXPORT_SYMBOL(inode_dio_wait);
void inode_set_flags(struct inode *inode, unsigned int flags,
unsigned int mask)
{
- unsigned int old_flags, new_flags;
-
WARN_ON_ONCE(flags & ~mask);
- do {
- old_flags = READ_ONCE(inode->i_flags);
- new_flags = (old_flags & ~mask) | flags;
- } while (unlikely(cmpxchg(&inode->i_flags, old_flags,
- new_flags) != old_flags));
+ set_mask_bits(&inode->i_flags, mask, flags);
}
EXPORT_SYMBOL(inode_set_flags);
--
2.7.4
Cc: Alexander Viro <[email protected]>
Cc: Peter Zijlstra (Intel) <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/g/[email protected]
Acked-by: Oleg Nesterov <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>
---
fs/exec.c | 7 +------
1 file changed, 1 insertion(+), 6 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index fb72d36f7823..df7f05362283 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1944,15 +1944,10 @@ EXPORT_SYMBOL(set_binfmt);
*/
void set_dumpable(struct mm_struct *mm, int value)
{
- unsigned long old, new;
-
if (WARN_ON((unsigned)value > SUID_DUMP_ROOT))
return;
- do {
- old = READ_ONCE(mm->flags);
- new = (old & ~MMF_DUMPABLE_MASK) | value;
- } while (cmpxchg(&mm->flags, old, new) != old);
+ set_mask_bits(&mm->flags, MMF_DUMPABLE_MASK, value);
}
SYSCALL_DEFINE3(execve,
--
2.7.4
| > Also, set_mask_bits is used in fs quite a bit and we can possibly come up
| > with a generic llsc based implementation (w/o the cmpxchg loop)
|
| May I also suggest changing the return value of set_mask_bits() to old.
|
| You can compute the new value given old, but you cannot compute the old
| value given new, therefore old is the better return value. Also, no
| current user seems to use the return value, so changing it is without
| risk.
Link: http://lkml.kernel.org/g/[email protected]
Suggested-by: Peter Zijlstra <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Vineet Gupta <[email protected]>
---
include/linux/bitops.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 705f7c442691..602af23b98c7 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
new__ = (old__ & ~mask__) | bits__; \
} while (cmpxchg(ptr, old__, new__) != old__); \
\
- new__; \
+ old__; \
})
#endif
--
2.7.4
On 1/10/19 4:26 PM, Vineet Gupta wrote:
> Cc: Alexander Viro <[email protected]>
> Cc: Peter Zijlstra (Intel) <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Link: http://lkml.kernel.org/g/[email protected]
> Acked-by: Oleg Nesterov <[email protected]>
> Signed-off-by: Vineet Gupta <[email protected]>
Reviewed-by: Anthony Yznaga <[email protected]>
On 1/10/19 4:26 PM, Vineet Gupta wrote:
> | > Also, set_mask_bits is used in fs quite a bit and we can possibly come up
> | > with a generic llsc based implementation (w/o the cmpxchg loop)
> |
> | May I also suggest changing the return value of set_mask_bits() to old.
> |
> | You can compute the new value given old, but you cannot compute the old
> | value given new, therefore old is the better return value. Also, no
> | current user seems to use the return value, so changing it is without
> | risk.
>
> Link: http://lkml.kernel.org/g/[email protected]
> Suggested-by: Peter Zijlstra <[email protected]>
> Cc: Miklos Szeredi <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Jani Nikula <[email protected]>
> Cc: Chris Wilson <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Will Deacon <[email protected]>
> Signed-off-by: Vineet Gupta <[email protected]>
>
Reviewed-by: Anthony Yznaga <[email protected]>
On 1/10/19 4:26 PM, Vineet Gupta wrote:
> It seems that 5f16f3225b0624 and 00a1a053ebe5, both with same commitlog
> ("ext4: atomically set inode->i_flags in ext4_set_inode_flags()")
> introduced the set_mask_bits API, but somehow missed not using it in
> ext4 in the end
>
> Also, set_mask_bits is used in fs quite a bit and we can possibly come up
> with a generic llsc based implementation (w/o the cmpxchg loop)
>
> Cc: Alexander Viro <[email protected]>
> Cc: Theodore Ts'o <[email protected]>
> Cc: Peter Zijlstra (Intel) <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: Vineet Gupta <[email protected]>
>
Reviewed-by: Anthony Yznaga <[email protected]>
On Thu, Jan 10, 2019 at 04:26:27PM -0800, Vineet Gupta wrote:
> @@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
> new__ = (old__ & ~mask__) | bits__; \
> } while (cmpxchg(ptr, old__, new__) != old__); \
diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 705f7c442691..2060d26a35f5 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -241,10 +241,10 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
const typeof(*(ptr)) mask__ = (mask), bits__ = (bits); \
typeof(*(ptr)) old__, new__; \
\
+ old__ = READ_ONCE(*(ptr)); \
do { \
- old__ = READ_ONCE(*(ptr)); \
new__ = (old__ & ~mask__) | bits__; \
- } while (cmpxchg(ptr, old__, new__) != old__); \
+ } while (!try_cmpxchg(ptr, &old__, new__)); \
\
new__; \
})
While there you probably want something like the above... although,
looking at it now, we seem to have 'forgotten' to add try_cmpxchg to the
generic code :/
On 1/11/19 1:24 AM, Peter Zijlstra wrote:
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 705f7c442691..2060d26a35f5 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -241,10 +241,10 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
> const typeof(*(ptr)) mask__ = (mask), bits__ = (bits); \
> typeof(*(ptr)) old__, new__; \
> \
> + old__ = READ_ONCE(*(ptr)); \
> do { \
> - old__ = READ_ONCE(*(ptr)); \
> new__ = (old__ & ~mask__) | bits__; \
> - } while (cmpxchg(ptr, old__, new__) != old__); \
> + } while (!try_cmpxchg(ptr, &old__, new__)); \
> \
> new__; \
> })
>
>
> While there you probably want something like the above...
As a separate change perhaps so that a revert (unlikely as it might be) could be
done with less pain.
> although,
> looking at it now, we seem to have 'forgotten' to add try_cmpxchg to the
> generic code :/
So it _has_ to be a separate change ;-)
But can we even provide a sane generic try_cmpxchg. The asm-generic cmpxchg relies
on local irq save etc so it is clearly only to prevent a new arch from failing to
compile. atomic*_cmpxchg() is different story since atomics have to be provided by
arch.
Anyhow what is more interesting is the try_cmpxchg API itself. So commit
a9ebf306f52c756 introduced/use of try_cmpxchg(), which indeed makes the looping
"nicer" to read and obvious code gen improvements.
So,
for (;;) {
new = val $op $imm;
old = cmpxchg(ptr, val, new);
if (old == val)
break;
val = old;
}
becomes
do {
} while (!try_cmpxchg(ptr, &val, val $op $imm));
But on pure LL/SC retry based arches, we still end up with generated code having 2
loops. We discussed something similar a while back: see [1]
First loop is inside inline asm to retry LL/SC and the outer one due to code
above. Explicit return of try_cmpxchg() means setting up a register with a boolean
status of cmpxchg (AFAIKR ARMv7 already does that but ARC e.g. uses a CPU flag
thus requires an additional insn or two). We could arguably remove the inline asm
loop and retry LL/SC from the outer loop, but it seems cleaner to keep the retry
where it belongs.
Also under the hood, try_cmpxchg() would end up re-reading it for the issue fixed
by commit 44fe84459faf1a.
Heck, it would all be simpler if we could express this w/o use of cmpxchg.
try_some_op(ptr, &val, val $op $imm);
P.S. the horrible API name is for indicative purposes only
This would remove the outer loop completely, also avoid any re-reads due to the
semantics of cmpxchg etc.
[1] https://www.spinics.net/lists/kernel/msg2029217.html
On Thu, Jan 10, 2019 at 04:26:27PM -0800, Vineet Gupta wrote:
> | > Also, set_mask_bits is used in fs quite a bit and we can possibly come up
> | > with a generic llsc based implementation (w/o the cmpxchg loop)
> |
> | May I also suggest changing the return value of set_mask_bits() to old.
> |
> | You can compute the new value given old, but you cannot compute the old
> | value given new, therefore old is the better return value. Also, no
> | current user seems to use the return value, so changing it is without
> | risk.
>
> Link: http://lkml.kernel.org/g/[email protected]
> Suggested-by: Peter Zijlstra <[email protected]>
> Cc: Miklos Szeredi <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Jani Nikula <[email protected]>
> Cc: Chris Wilson <[email protected]>
> Cc: Andrew Morton <[email protected]>
> Cc: Will Deacon <[email protected]>
> Signed-off-by: Vineet Gupta <[email protected]>
> ---
> include/linux/bitops.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 705f7c442691..602af23b98c7 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -246,7 +246,7 @@ static __always_inline void __assign_bit(long nr, volatile unsigned long *addr,
> new__ = (old__ & ~mask__) | bits__; \
> } while (cmpxchg(ptr, old__, new__) != old__); \
> \
> - new__; \
> + old__; \
> })
> #endif
Acked-by: Will Deacon <[email protected]>
May also explain why no in-tree users appear to use the return value!
Will