It turned out that DEBUG_SLAB_LEAK is still broken even after recent
recue efforts that when there is a large number of objects like
kmemleak_object which is normal on a debug kernel,
# grep kmemleak /proc/slabinfo
kmemleak_object 2243606 3436210 ...
reading /proc/slab_allocators could easily loop forever while processing
the kmemleak_object cache and any additional freeing or allocating
objects will trigger a reprocessing. To make a situation worse,
soft-lockups could easily happen in this sitatuion which will call
printk() to allocate more kmemleak objects to guarantee an infinite
loop.
Also, since it seems no one had noticed when it was totally broken
more than 2-year ago - see the commit fcf88917dd ("slab: fix a crash
by reading /proc/slab_allocators"), probably nobody cares about it
anymore due to the decline of the SLAB. Just remove it entirely.
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Qian Cai <cai@lca.pw>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull nommu generic uaccess updates from Arnd Bergmann:
"asm-generic: kill <asm/segment.h> and improve nommu generic uaccess helpers
Christoph Hellwig writes:
This is a series doing two somewhat interwinded things. It improves
the asm-generic nommu uaccess helper to optionally be entirely
generic and not require any arch helpers for the actual uaccess.
For the generic uaccess.h to actually be generically useful I also
had to kill off the mess we made of <asm/segment.h>, which really
shouldn't exist on most architectures"
* tag 'asm-generic-nommu' of git://git.kernel.org/pub/scm/linux/kernel/git/arnd/asm-generic:
asm-generic: optimize generic uaccess for 8-byte loads and stores
asm-generic: provide entirely generic nommu uaccess
arch: mostly remove <asm/segment.h>
asm-generic: don't include <asm/segment.h> from <asm/uaccess.h>
The kernel has only two users of proc_do_large_bitmap(), the kernel CPU
watchdog, and the ip_local_reserved_ports. Refer to watchdog_cpumask
and ip_local_reserved_ports in Documentation for further details on
these. When you input a large buffer into these, when it is larger than
PAGE_SIZE- 1, the input data gets misparsed, and the user get
incorrectly informed that the desired input value was set. This commit
implements a test which mimics and exploits that use case, it uses a
bitmap size, as in the watchdog case. The bitmap is used to test the
bitmap proc handler, proc_do_large_bitmap().
The next commit fixes this issue.
[akpm@linux-foundation.org: move proc_do_large_bitmap() export to EOF]
[mcgrof@kernel.org: use new target description for backward compatibility]
[mcgrof@kernel.org: augment test number to 50, ran into issues with bash string comparisons when testing up to 50 cases.]
[mcgrof@kernel.org: introduce and use verify_diff_proc_file() to use diff]
[mcgrof@kernel.org: use mktemp for tmp file]
[mcgrof@kernel.org: merge shell test and C code]
[mcgrof@kernel.org: commit log love]
[mcgrof@kernel.org: export proc_do_large_bitmap() to allow for the test
[mcgrof@kernel.org: check for the return value when writing to the proc file]
Link: http://lkml.kernel.org/r/20190320222831.8243-6-mcgrof@kernel.org
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "lib: rework bitmap_parselist and tests", v5.
bitmap_parselist has been evolved from a pretty simple idea for long and
now lacks for refactoring. It is not structured, has nested loops and a
set of opaque-named variables.
Things are more complicated because bitmap_parselist() is a part of user
interface, and its behavior should not change.
In this patchset
- bitmap_parselist_user() made a wrapper on bitmap_parselist();
- bitmap_parselist() reworked (patch 2);
- time measurement in test_bitmap_parselist switched to ktime_get
(patch 3);
- new tests introduced (patch 4), and
- bitmap_parselist_user() testing enabled with the same testset as
bitmap_parselist() (patch 5).
This patch (of 5):
Currently we parse user data byte after byte which leads to
overcomplification of parsing algorithm. The only user of
bitmap_parselist_user() is not performance-critical, and so we can
duplicate user data to kernel buffer and simply call bitmap_parselist().
This rework lets us unify and simplify bitmap_parselist() and
bitmap_parselist_user(), which is done in the following patch.
Link: http://lkml.kernel.org/r/20190405173211.11373-2-ynorov@marvell.com
Signed-off-by: Yury Norov <ynorov@marvell.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Mike Travis <travis@sgi.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
CONFIG_RETPOLINE has severely degraded indirect function call
performance, so it's worth putting some effort into reducing the number
of times cmp() is called.
This patch avoids badly unbalanced merges on unlucky input sizes. It
slightly increases the code size, but saves an average of 0.2*n calls to
cmp().
x86-64 code size 739 -> 803 bytes (+64)
Unfortunately, there's not a lot of low-hanging fruit in a merge sort;
it already performs only n*log2(n) - K*n + O(1) compares. The leading
coefficient is already at the theoretical limit (log2(n!) corresponds to
K=1.4427), so we're fighting over the linear term, and the best
mergesort can do is K=1.2645, achieved when n is a power of 2.
The differences between mergesort variants appear when n is *not* a
power of 2; K is a function of the fractional part of log2(n). Top-down
mergesort does best of all, achieving a minimum K=1.2408, and an average
(over all sizes) K=1.248. However, that requires knowing the number of
entries to be sorted ahead of time, and making a full pass over the
input to count it conflicts with a second performance goal, which is
cache blocking.
Obviously, we have to read the entire list into L1 cache at some point,
and performance is best if it fits. But if it doesn't fit, each full
pass over the input causes a cache miss per element, which is
undesirable.
While textbooks explain bottom-up mergesort as a succession of merging
passes, practical implementations do merging in depth-first order: as
soon as two lists of the same size are available, they are merged. This
allows as many merge passes as possible to fit into L1; only the final
few merges force cache misses.
This cache-friendly depth-first merge order depends on us merging the
beginning of the input as much as possible before we've even seen the
end of the input (and thus know its size).
The simple eager merge pattern causes bad performance when n is just
over a power of 2. If n=1028, the final merge is between 1024- and
4-element lists, which is wasteful of comparisons. (This is actually
worse on average than n=1025, because a 1204:1 merge will, on average,
end after 512 compares, while 1024:4 will walk 4/5 of the list.)
Because of this, bottom-up mergesort achieves K < 0.5 for such sizes,
and has an average (over all sizes) K of around 1. (My experiments show
K=1.01, while theory predicts K=0.965.)
There are "worst-case optimal" variants of bottom-up mergesort which
avoid this bad performance, but the algorithms given in the literature,
such as queue-mergesort and boustrodephonic mergesort, depend on the
breadth-first multi-pass structure that we are trying to avoid.
This implementation is as eager as possible while ensuring that all
merge passes are at worst 1:2 unbalanced. This achieves the same
average K=1.207 as queue-mergesort, which is 0.2*n better then
bottom-up, and only 0.04*n behind top-down mergesort.
Specifically, defers merging two lists of size 2^k until it is known
that there are 2^k additional inputs following. This ensures that the
final uneven merges triggered by reaching the end of the input will be
at worst 2:1. This will avoid cache misses as long as 3*2^k elements
fit into the cache.
(I confess to being more than a little bit proud of how clean this code
turned out. It took a lot of thinking, but the resultant inner loop is
very simple and efficient.)
Refs:
Bottom-up Mergesort: A Detailed Analysis
Wolfgang Panny, Helmut Prodinger
Algorithmica 14(4):340--354, October 1995
https://doi.org/10.1007/BF01294131https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.6.5260
The cost distribution of queue-mergesort, optimal mergesorts, and
power-of-two rules
Wei-Mei Chen, Hsien-Kuei Hwang, Gen-Huey Chen
Journal of Algorithms 30(2); Pages 423--448, February 1999
https://doi.org/10.1006/jagm.1998.0986https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.4.5380
Queue-Mergesort
Mordecai J. Golin, Robert Sedgewick
Information Processing Letters, 48(5):253--259, 10 December 1993
https://doi.org/10.1016/0020-0190(93)90088-qhttps://sci-hub.tw/10.1016/0020-0190(93)90088-Q
Feedback from Rasmus Villemoes <linux@rasmusvillemoes.dk>.
Link: http://lkml.kernel.org/r/fd560853cc4dca0d0f02184ffa888b4c1be89abc.1552704200.git.lkml@sdf.org
Signed-off-by: George Spelvin <lkml@sdf.org>
Acked-by: Andrey Abramov <st5pub@yandex.ru>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Daniel Wagner <daniel.wagner@siemens.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Don Mullis <don.mullis@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Rather than a fixed-size array of pending sorted runs, use the ->prev
links to keep track of things. This reduces stack usage, eliminates
some ugly overflow handling, and reduces the code size.
Also:
* merge() no longer needs to handle NULL inputs, so simplify.
* The same applies to merge_and_restore_back_links(), which is renamed
to the less ponderous merge_final(). (It's a static helper function,
so we don't need a super-descriptive name; comments will do.)
* Document the actual return value requirements on the (*cmp)()
function; some callers are already using this feature.
x86-64 code size 1086 -> 739 bytes (-347)
(Yes, I see checkpatch complaining about no space after comma in
"__attribute__((nonnull(2,3,4,5)))". Checkpatch is wrong.)
Feedback from Rasmus Villemoes, Andy Shevchenko and Geert Uytterhoeven.
[akpm@linux-foundation.org: remove __pure usage due to mysterious warning]
Link: http://lkml.kernel.org/r/f63c410e0ff76009c9b58e01027e751ff7fdb749.1552704200.git.lkml@sdf.org
Signed-off-by: George Spelvin <lkml@sdf.org>
Acked-by: Andrey Abramov <st5pub@yandex.ru>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Daniel Wagner <daniel.wagner@siemens.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Don Mullis <don.mullis@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This uses fewer comparisons than the previous code (approaching half as
many for large random inputs), but produces identical results; it
actually performs the exact same series of swap operations.
Specifically, it reduces the average number of compares from
2*n*log2(n) - 3*n + o(n)
to
n*log2(n) + 0.37*n + o(n).
This is still 1.63*n worse than glibc qsort() which manages n*log2(n) -
1.26*n, but at least the leading coefficient is correct.
Standard heapsort, when sifting down, performs two comparisons per
level: one to find the greater child, and a second to see if the current
node should be exchanged with that child.
Bottom-up heapsort observes that it's better to postpone the second
comparison and search for the leaf where -infinity would be sent to,
then search back *up* for the current node's destination.
Since sifting down usually proceeds to the leaf level (that's where half
the nodes are), this does O(1) second comparisons rather than log2(n).
That saves a lot of (expensive since Spectre) indirect function calls.
The one time it's worse than the previous code is if there are large
numbers of duplicate keys, when the top-down algorithm is O(n) and
bottom-up is O(n log n). For distinct keys, it's provably always
better, doing 1.5*n*log2(n) + O(n) in the worst case.
(The code is not significantly more complex. This patch also merges the
heap-building and -extracting sift-down loops, resulting in a net code
size savings.)
x86-64 code size 885 -> 767 bytes (-118)
(I see the checkpatch complaint about "else if (n -= size)". The
alternative is significantly uglier.)
Link: http://lkml.kernel.org/r/2de8348635a1a421a72620677898c7fd5bd4b19d.1552704200.git.lkml@sdf.org
Signed-off-by: George Spelvin <lkml@sdf.org>
Acked-by: Andrey Abramov <st5pub@yandex.ru>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Daniel Wagner <daniel.wagner@siemens.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Don Mullis <don.mullis@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Patch series "lib/sort & lib/list_sort: faster and smaller", v2.
Because CONFIG_RETPOLINE has made indirect calls much more expensive, I
thought I'd try to reduce the number made by the library sort functions.
The first three patches apply to lib/sort.c.
Patch #1 is a simple optimization. The built-in swap has special cases
for aligned 4- and 8-byte objects. But those are almost never used;
most calls to sort() work on larger structures, which fall back to the
byte-at-a-time loop. This generalizes them to aligned *multiples* of 4
and 8 bytes. (If nothing else, it saves an awful lot of energy by not
thrashing the store buffers as much.)
Patch #2 grabs a juicy piece of low-hanging fruit. I agree that nice
simple solid heapsort is preferable to more complex algorithms (sorry,
Andrey), but it's possible to implement heapsort with far fewer
comparisons (50% asymptotically, 25-40% reduction for realistic sizes)
than the way it's been done up to now. And with some care, the code
ends up smaller, as well. This is the "big win" patch.
Patch #3 adds the same sort of indirect call bypass that has been added
to the net code of late. The great majority of the callers use the
builtin swap functions, so replace the indirect call to sort_func with a
(highly preditable) series of if() statements. Rather surprisingly,
this decreased code size, as the swap functions were inlined and their
prologue & epilogue code eliminated.
lib/list_sort.c is a bit trickier, as merge sort is already close to
optimal, and we don't want to introduce triumphs of theory over
practicality like the Ford-Johnson merge-insertion sort.
Patch #4, without changing the algorithm, chops 32% off the code size
and removes the part[MAX_LIST_LENGTH+1] pointer array (and the
corresponding upper limit on efficiently sortable input size).
Patch #5 improves the algorithm. The previous code is already optimal
for power-of-two (or slightly smaller) size inputs, but when the input
size is just over a power of 2, there's a very unbalanced final merge.
There are, in the literature, several algorithms which solve this, but
they all depend on the "breadth-first" merge order which was replaced by
commit 835cc0c847 with a more cache-friendly "depth-first" order.
Some hard thinking came up with a depth-first algorithm which defers
merges as little as possible while avoiding bad merges. This saves
0.2*n compares, averaged over all sizes.
The code size increase is minimal (64 bytes on x86-64, reducing the net
savings to 26%), but the comments expanded significantly to document the
clever algorithm.
TESTING NOTES: I have some ugly user-space benchmarking code which I
used for testing before moving this code into the kernel. Shout if you
want a copy.
I'm running this code right now, with CONFIG_TEST_SORT and
CONFIG_TEST_LIST_SORT, but I confess I haven't rebooted since the last
round of minor edits to quell checkpatch. I figure there will be at
least one round of comments and final testing.
This patch (of 5):
Rather than having special-case swap functions for 4- and 8-byte
objects, special-case aligned multiples of 4 or 8 bytes. This speeds up
most users of sort() by avoiding fallback to the byte copy loop.
Despite what ca96ab859a ("lib/sort: Add 64 bit swap function") claims,
very few users of sort() sort pointers (or pointer-sized objects); most
sort structures containing at least two words. (E.g.
drivers/acpi/fan.c:acpi_fan_get_fps() sorts an array of 40-byte struct
acpi_fan_fps.)
The functions also got renamed to reflect the fact that they support
multiple words. In the great tradition of bikeshedding, the names were
by far the most contentious issue during review of this patch series.
x86-64 code size 872 -> 886 bytes (+14)
With feedback from Andy Shevchenko, Rasmus Villemoes and Geert
Uytterhoeven.
Link: http://lkml.kernel.org/r/f24f932df3a7fa1973c1084154f1cea596bcf341.1552704200.git.lkml@sdf.org
Signed-off-by: George Spelvin <lkml@sdf.org>
Acked-by: Andrey Abramov <st5pub@yandex.ru>
Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Daniel Wagner <daniel.wagner@siemens.com>
Cc: Don Mullis <don.mullis@gmail.com>
Cc: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
The bitmap_remap, _bitremap, _onto and _fold functions are only used,
via their node_ wrappers, in mm/mempolicy.c, which is only built for
CONFIG_NUMA. The helper bitmap_ord_to_pos used by these functions is
global, but its only external caller is node_random() in lib/nodemask.c,
which is also guarded by CONFIG_NUMA.
For !CONFIG_NUMA:
add/remove: 0/6 grow/shrink: 0/0 up/down: 0/-621 (-621)
Function old new delta
bitmap_pos_to_ord 20 - -20
bitmap_ord_to_pos 70 - -70
bitmap_bitremap 81 - -81
bitmap_fold 113 - -113
bitmap_onto 123 - -123
bitmap_remap 214 - -214
Total: Before=4776, After=4155, chg -13.00%
Link: http://lkml.kernel.org/r/20190329205353.6010-2-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Pull printk fixup from Petr Mladek:
"Replace the problematic probe_kernel_read() with original simple
pointer checks in vsprintf()"
* tag 'printk-for-5.2-fixes' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/pmladek/printk:
vsprintf: Do not break early boot with probing addresses
Qian Cai
Linus Torvalds
Ingo Molnar
Eric Sandeen
Sinan Kaya
Andrew Morton
Yury Norov
Andy Shevchenko
George Spelvin
Davidlohr Bueso
Rasmus Villemoes
Masahiro Yamada
Ira Weiny