linux-toradex.git/include/linux/refcount.h, branch v5.10-rc3

locking/refcount: move kernel-doc markups to the proper place

2020-10-28T17:41:15+00:00

Changeset a435b9a14356 ("locking/refcount: Provide __refcount API to obtain the old value")
added a set of functions starting with __ that have a new
parameter, adding a series of new warnings:

	$ ./scripts/kernel-doc -none include/linux/refcount.h
	include/linux/refcount.h:169: warning: Function parameter or member 'oldp' not described in '__refcount_add_not_zero'
	include/linux/refcount.h:208: warning: Function parameter or member 'oldp' not described in '__refcount_add'
	include/linux/refcount.h:239: warning: Function parameter or member 'oldp' not described in '__refcount_inc_not_zero'
	include/linux/refcount.h:261: warning: Function parameter or member 'oldp' not described in '__refcount_inc'
	include/linux/refcount.h:291: warning: Function parameter or member 'oldp' not described in '__refcount_sub_and_test'
	include/linux/refcount.h:327: warning: Function parameter or member 'oldp' not described in '__refcount_dec_and_test'
	include/linux/refcount.h:347: warning: Function parameter or member 'oldp' not described in '__refcount_dec'

The issue is that the kernel-doc markups are now misplaced,
as they should be added just before the functions.

So, move the kernel-doc markups to the proper places,
in order to drop the warnings.

It should be noticed that git show produces a crappy output,
for this patch without "--patience" flag.

Fixes: a435b9a14356 ("locking/refcount: Provide __refcount API to obtain the old value")
Signed-off-by: Mauro Carvalho Chehab 
Link: https://lore.kernel.org/r/7985c31d1ace591bc5e1faa05c367f1295b78afd.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet

locking/refcount: Provide __refcount API to obtain the old value

2020-08-26T10:42:02+00:00

David requested means to obtain the old/previous value from the
refcount API for tracing purposes.

Duplicate (most of) the API as __refcount*() with an additional
'int *' argument into which, if !NULL, the old value will be stored.

Requested-by: David Howells 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Kees Cook 
Link: https://lkml.kernel.org/r/20200729111120.GA2638@hirez.programming.kicks-ass.net

locking/refcount: Document interaction with PID_MAX_LIMIT

2020-04-08T10:05:07+00:00

Document the circumstances under which refcount_t's saturation mechanism
works deterministically.

Acked-by: Kees Cook 
Acked-by: Will Deacon 
Signed-off-by: Jann Horn 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Ingo Molnar 
Link: https://lkml.kernel.org/r/20200303105427.260620-1-jannh@google.com

locking/refcount: Consolidate implementations of refcount_t

2019-11-25T08:15:32+00:00

The generic implementation of refcount_t should be good enough for
everybody, so remove ARCH_HAS_REFCOUNT and REFCOUNT_FULL entirely,
leaving the generic implementation enabled unconditionally.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Acked-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-9-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Consolidate REFCOUNT_{MAX,SATURATED} definitions

2019-11-25T08:15:27+00:00

The definitions of REFCOUNT_MAX and REFCOUNT_SATURATED are the same,
regardless of CONFIG_REFCOUNT_FULL, so consolidate them into a single
pair of definitions.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-8-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Move saturation warnings out of line

2019-11-25T08:15:21+00:00

Having the refcount saturation and warnings inline bloats the text,
despite the fact that these paths should never be executed in normal
operation.

Move the refcount saturation and warnings out of line to reduce the
image size when refcount_t checking is enabled. Relative to an x86_64
defconfig, the sizes reported by bloat-o-meter are:

 # defconfig+REFCOUNT_FULL, inline saturation (i.e. before this patch)
 Total: Before=14762076, After=14915442, chg +1.04%

 # defconfig+REFCOUNT_FULL, out-of-line saturation (i.e. after this patch)
 Total: Before=14762076, After=14835497, chg +0.50%

A side-effect of this change is that we now only get one warning per
refcount saturation type, rather than one per problematic call-site.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-7-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Improve performance of generic REFCOUNT_FULL code

2019-11-25T08:15:10+00:00

Rewrite the generic REFCOUNT_FULL implementation so that the saturation
point is moved to INT_MIN / 2. This allows us to defer the sanity checks
until after the atomic operation, which removes many uses of cmpxchg()
in favour of atomic_fetch_{add,sub}().

Some crude perf results obtained from lkdtm show substantially less
overhead, despite the checking:

 $ perf stat -r 3 -B -- echo {ATOMIC,REFCOUNT}_TIMING >/sys/kernel/debug/provoke-crash/DIRECT

 # arm64
 ATOMIC_TIMING:                                      46.50451 +- 0.00134 seconds time elapsed  ( +-  0.00% )
 REFCOUNT_TIMING (REFCOUNT_FULL, mainline):          77.57522 +- 0.00982 seconds time elapsed  ( +-  0.01% )
 REFCOUNT_TIMING (REFCOUNT_FULL, this series):       48.7181  +- 0.0256  seconds time elapsed  ( +-  0.05% )

 # x86
 ATOMIC_TIMING:                                      31.6225 +- 0.0776 seconds time elapsed  ( +-  0.25% )
 REFCOUNT_TIMING (!REFCOUNT_FULL, mainline/x86 asm): 31.6689 +- 0.0901 seconds time elapsed  ( +-  0.28% )
 REFCOUNT_TIMING (REFCOUNT_FULL, mainline):          53.203  +- 0.138  seconds time elapsed  ( +-  0.26% )
 REFCOUNT_TIMING (REFCOUNT_FULL, this series):       31.7408 +- 0.0486 seconds time elapsed  ( +-  0.15% )

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Tested-by: Jan Glauber 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-6-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Move the bulk of the REFCOUNT_FULL implementation into the header

2019-11-25T08:15:06+00:00

In an effort to improve performance of the REFCOUNT_FULL implementation,
move the bulk of its functions into linux/refcount.h. This allows them
to be inlined in the same way as if they had been provided via
CONFIG_ARCH_HAS_REFCOUNT.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-5-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Remove unused refcount_*_checked() variants

2019-11-25T08:15:03+00:00

The full-fat refcount implementation is exposed via a set of functions
suffixed with "_checked()", the idea being that code can choose to use
the more expensive, yet more secure implementation on a case-by-case
basis.

In reality, this hasn't happened, so with a grand total of zero users,
let's remove the checked variants for now by simply dropping the suffix
and predicating the out-of-line functions on CONFIG_REFCOUNT_FULL=y.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-4-will@kernel.org
Signed-off-by: Ingo Molnar

locking/refcount: Ensure integer operands are treated as signed

2019-11-25T08:14:57+00:00

In preparation for changing the saturation point of REFCOUNT_FULL to
INT_MIN/2, change the type of integer operands passed into the API
from 'unsigned int' to 'int' so that we can avoid casting during
comparisons when we don't want to fall foul of C integral conversion
rules for signed and unsigned types.

Since the kernel is compiled with '-fno-strict-overflow', we don't need
to worry about the UB introduced by signed overflow here. Furthermore,
we're already making heavy use of the atomic_t API, which operates
exclusively on signed types.

Signed-off-by: Will Deacon 
Reviewed-by: Ard Biesheuvel 
Reviewed-by: Kees Cook 
Tested-by: Hanjun Guo 
Cc: Ard Biesheuvel 
Cc: Elena Reshetova 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Link: https://lkml.kernel.org/r/20191121115902.2551-3-will@kernel.org
Signed-off-by: Ingo Molnar