1. 01 Jun, 2016 8 commits
    • Hans de Goede's avatar
      usb: quirks: Add no-lpm quirk for Acer C120 LED Projector · 32cb0b37
      Hans de Goede authored
      The Acer C120 LED Projector is a USB-3 connected pico projector which
      takes both its power and video data from USB-3.
      
      In combination with some hubs this device does not play well with
      lpm, so disable lpm for it.
      Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
      Cc: stable <stable@vger.kernel.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      32cb0b37
    • Hans de Goede's avatar
      usb: quirks: Fix sorting · 81099f97
      Hans de Goede authored
      Properly sort all the entries by vendor id.
      Signed-off-by: default avatarHans de Goede <hdegoede@redhat.com>
      Cc: stable <stable@vger.kernel.org>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      81099f97
    • Mathias Nyman's avatar
      xhci: fix platform quirks overwrite regression in 4.7-rc1 · 757de492
      Mathias Nyman authored
      commit b1c127ae ("usb: host: xhci: plat: make use of new methods in
      xhci_plat_priv") sets xhci->quirks before calling xhci_gen_setup(), which
      will overwrite them.
      
      Don't overwite the quirks, just add the new ones
      
      Fixes: b1c127ae ("usb: host: xhci: plat: make use of new methods in xhci_plat_priv")
      Reported-by: default avatarYoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
      Cc: Felipe Balbi <felipe.balbi@linux.intel.com>
      Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      757de492
    • Thomas Petazzoni's avatar
      usb: xhci-plat: properly handle probe deferral for devm_clk_get() · de95c40d
      Thomas Petazzoni authored
      On some platforms, the clocks might be registered by a platform
      driver. When this is the case, the clock platform driver may very well
      be probed after xhci-plat, in which case the first probe() invocation
      of xhci-plat will receive -EPROBE_DEFER as the return value of
      devm_clk_get().
      
      The current code handles that as a normal error, and simply assumes
      that this means that the system doesn't have a clock for the XHCI
      controller, and continues probing without calling
      clk_prepare_enable(). Unfortunately, this doesn't work on systems
      where the XHCI controller does have a clock, but that clock is
      provided by another platform driver. In order to fix this situation,
      we handle the -EPROBE_DEFER error condition specially, and abort the
      XHCI controller probe(). It will be retried later automatically, the
      clock will be available, devm_clk_get() will succeed, and the probe()
      will continue with the clock prepared and enabled as expected.
      
      In practice, such issue is seen on the ARM64 Marvell 7K/8K platform,
      where the clocks are registered by a platform driver.
      
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarThomas Petazzoni <thomas.petazzoni@free-electrons.com>
      Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      de95c40d
    • Mathias Nyman's avatar
      xhci: Fix handling timeouted commands on hosts in weird states. · 3425aa03
      Mathias Nyman authored
      If commands timeout we mark them for abortion, then stop the command
      ring, and turn the commands to no-ops and finally restart the command
      ring.
      
      If the host is working properly the no-op commands will finish and
      pending completions are called.
      If we notice the host is failing, driver clears the command ring and
      completes, deletes and frees all pending commands.
      
      There are two separate cases reported where host is believed to work
      properly but is not. In the first case we successfully stop the ring
      but no abort or stop command ring event is ever sent and host locks up.
      
      The second case is if a host is removed, command times out and driver
      believes the ring is stopped, and assumes it will be restarted, but
      actually ends up timing out on the same command forever.
      If one of the pending commands has the xhci->mutex held it will block
      xhci_stop() in the remove codepath which otherwise would cleanup pending
      commands.
      
      Add a check that clears all pending commands in case host is removed,
      or we are stuck timing out on the same command. Also restart the
      command timeout timer when stopping the command ring to ensure we
      recive an ring stop/abort event.
      
      Cc: stable <stable@vger.kernel.org>
      Tested-by: default avatarJoe Lawrence <joe.lawrence@stratus.com>
      Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      3425aa03
    • Gabriel Krisman Bertazi's avatar
      xhci: Cleanup only when releasing primary hcd · 27a41a83
      Gabriel Krisman Bertazi authored
      Under stress occasions some TI devices might not return early when
      reading the status register during the quirk invocation of xhci_irq made
      by usb_hcd_pci_remove.  This means that instead of returning, we end up
      handling this interruption in the middle of a shutdown.  Since
      xhci->event_ring has already been freed in xhci_mem_cleanup, we end up
      accessing freed memory, causing the Oops below.
      
      commit 8c24d6d7 ("usb: xhci: stop everything on the first call to
      xhci_stop") is the one that changed the instant in which we clean up the
      event queue when stopping a device.  Before, we didn't call
      xhci_mem_cleanup at the first time xhci_stop is executed (for the shared
      HCD), instead, we only did it after the invocation for the primary HCD,
      much later at the removal path.  The code flow for this oops looks like
      this:
      
      xhci_pci_remove()
      	usb_remove_hcd(xhci->shared)
      	        xhci_stop(xhci->shared)
       			xhci_halt()
      			xhci_mem_cleanup(xhci);  // Free the event_queue
      	usb_hcd_pci_remove(primary)
      		xhci_irq()  // Access the event_queue if STS_EINT is set. Crash.
      		xhci_stop()
      			xhci_halt()
      			// return early
      
      The fix modifies xhci_stop to only cleanup the xhci data when releasing
      the primary HCD.  This way, we still have the event_queue configured
      when invoking xhci_irq.  We still halt the device on the first call to
      xhci_stop, though.
      
      I could reproduce this issue several times on the mainline kernel by
      doing a bind-unbind stress test with a specific storage gadget attached.
      I also ran the same test over-night with my patch applied and didn't
      observe the issue anymore.
      
      [  113.334124] Unable to handle kernel paging request for data at address 0x00000028
      [  113.335514] Faulting instruction address: 0xd00000000d4f767c
      [  113.336839] Oops: Kernel access of bad area, sig: 11 [#1]
      [  113.338214] SMP NR_CPUS=1024 NUMA PowerNV
      
      [c000000efe47ba90] c000000000720850 usb_hcd_irq+0x50/0x80
      [c000000efe47bac0] c00000000073d328 usb_hcd_pci_remove+0x68/0x1f0
      [c000000efe47bb00] d00000000daf0128 xhci_pci_remove+0x78/0xb0
      [xhci_pci]
      [c000000efe47bb30] c00000000055cf70 pci_device_remove+0x70/0x110
      [c000000efe47bb70] c00000000061c6bc __device_release_driver+0xbc/0x190
      [c000000efe47bba0] c00000000061c7d0 device_release_driver+0x40/0x70
      [c000000efe47bbd0] c000000000619510 unbind_store+0x120/0x150
      [c000000efe47bc20] c0000000006183c4 drv_attr_store+0x64/0xa0
      [c000000efe47bc60] c00000000039f1d0 sysfs_kf_write+0x80/0xb0
      [c000000efe47bca0] c00000000039e14c kernfs_fop_write+0x18c/0x1f0
      [c000000efe47bcf0] c0000000002e962c __vfs_write+0x6c/0x190
      [c000000efe47bd90] c0000000002eab40 vfs_write+0xc0/0x200
      [c000000efe47bde0] c0000000002ec85c SyS_write+0x6c/0x110
      [c000000efe47be30] c000000000009260 system_call+0x38/0x108
      Signed-off-by: default avatarGabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
      Cc: Roger Quadros <rogerq@ti.com>
      Cc: joel@jms.id.au
      Cc: stable@vger.kernel.org
      Reviewed-by: default avatarRoger Quadros <rogerq@ti.com>
      Cc: <stable@vger.kernel.org> #v4.3+
      Tested-by: default avatarJoel Stanley <joel@jms.id.au>
      Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
      Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
      27a41a83
    • Greg Kroah-Hartman's avatar
      Merge tag 'fixes-for-v4.7-rc2' of... · 6399232f
      Greg Kroah-Hartman authored
      Merge tag 'fixes-for-v4.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb into usb-linus
      
      Felipe writes:
      
      Here's the first set of fixes for v4.7-rc
      cycle. Nothing extra fancy this time around.
      
      Patches range from MS OS Descriptor usage fixes, to
      Clear Stall EP command fix on dwc3, to some f_fs
      fixes and out of bounds accesses on renesas driver.
      6399232f
    • John Youn's avatar
      usb: dwc3: Set the ClearPendIN bit on Clear Stall EP command · 50c763f8
      John Youn authored
      As of core revision 2.60a the recommended programming model is to set
      the ClearPendIN bit when issuing a Clear Stall EP command for IN
      endpoints. This is to prevent an issue where some (non-compliant) hosts
      may not send ACK TPs for pending IN transfers due to a mishandled error
      condition. Synopsys STAR 9000614252.
      Signed-off-by: default avatarJohn Youn <johnyoun@synopsys.com>
      Signed-off-by: default avatarFelipe Balbi <felipe.balbi@linux.intel.com>
      50c763f8
  2. 31 May, 2016 17 commits
  3. 29 May, 2016 3 commits
  4. 28 May, 2016 12 commits
    • Mikulas Patocka's avatar
      hpfs: implement the show_options method · 037369b8
      Mikulas Patocka authored
      The HPFS filesystem used generic_show_options to produce string that is
      displayed in /proc/mounts.  However, there is a problem that the options
      may disappear after remount.  If we mount the filesystem with option1
      and then remount it with option2, /proc/mounts should show both option1
      and option2, however it only shows option2 because the whole option
      string is replaced with replace_mount_options in hpfs_remount_fs.
      
      To fix this bug, implement the hpfs_show_options function that prints
      options that are currently selected.
      Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
      Cc: stable@vger.kernel.org
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      037369b8
    • Mikulas Patocka's avatar
      affs: fix remount failure when there are no options changed · 01d6e087
      Mikulas Patocka authored
      Commit c8f33d0b ("affs: kstrdup() memory handling") checks if the
      kstrdup function returns NULL due to out-of-memory condition.
      
      However, if we are remounting a filesystem with no change to
      filesystem-specific options, the parameter data is NULL.  In this case,
      kstrdup returns NULL (because it was passed NULL parameter), although no
      out of memory condition exists.  The mount syscall then fails with
      ENOMEM.
      
      This patch fixes the bug.  We fail with ENOMEM only if data is non-NULL.
      
      The patch also changes the call to replace_mount_options - if we didn't
      pass any filesystem-specific options, we don't call
      replace_mount_options (thus we don't erase existing reported options).
      
      Fixes: c8f33d0b ("affs: kstrdup() memory handling")
      Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
      Cc: stable@vger.kernel.org	# v4.1+
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      01d6e087
    • Mikulas Patocka's avatar
      hpfs: fix remount failure when there are no options changed · 44d51706
      Mikulas Patocka authored
      Commit ce657611 ("hpfs: kstrdup() out of memory handling") checks if
      the kstrdup function returns NULL due to out-of-memory condition.
      
      However, if we are remounting a filesystem with no change to
      filesystem-specific options, the parameter data is NULL.  In this case,
      kstrdup returns NULL (because it was passed NULL parameter), although no
      out of memory condition exists.  The mount syscall then fails with
      ENOMEM.
      
      This patch fixes the bug.  We fail with ENOMEM only if data is non-NULL.
      
      The patch also changes the call to replace_mount_options - if we didn't
      pass any filesystem-specific options, we don't call
      replace_mount_options (thus we don't erase existing reported options).
      
      Fixes: ce657611 ("hpfs: kstrdup() out of memory handling")
      Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
      Cc: stable@vger.kernel.org
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      44d51706
    • Linus Torvalds's avatar
      Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus · 4029632c
      Linus Torvalds authored
      Pull more MIPS updates from Ralf Baechle:
       "This is the secondnd batch of MIPS patches for 4.7. Summary:
      
        CPS:
         - Copy EVA configuration when starting secondary VPs.
      
        EIC:
         - Clear Status IPL.
      
        Lasat:
         - Fix a few off by one bugs.
      
        lib:
         - Mark intrinsics notrace.  Not only are the intrinsics
           uninteresting, it would cause infinite recursion.
      
        MAINTAINERS:
         - Add file patterns for MIPS BRCM device tree bindings.
         - Add file patterns for mips device tree bindings.
      
        MT7628:
         - Fix MT7628 pinmux typos.
         - wled_an pinmux gpio.
         - EPHY LEDs pinmux support.
      
        Pistachio:
         - Enable KASLR
      
        VDSO:
         - Build microMIPS VDSO for microMIPS kernels.
         - Fix aliasing warning by building with `-fno-strict-aliasing' for
           debugging but also tracing them might result in recursion.
      
        Misc:
         - Add missing FROZEN hotplug notifier transitions.
         - Fix clk binding example for varioius PIC32 devices.
         - Fix cpu interrupt controller node-names in the DT files.
         - Fix XPA CPU feature separation.
         - Fix write_gc0_* macros when writing zero.
         - Add inline asm encoding helpers.
         - Add missing VZ accessor microMIPS encodings.
         - Fix little endian microMIPS MSA encodings.
         - Add 64-bit HTW fields and fix its configuration.
         - Fix sigreturn via VDSO on microMIPS kernel.
         - Lots of typo fixes.
         - Add definitions of SegCtl registers and use them"
      
      * 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus: (49 commits)
        MIPS: Add missing FROZEN hotplug notifier transitions
        MIPS: Build microMIPS VDSO for microMIPS kernels
        MIPS: Fix sigreturn via VDSO on microMIPS kernel
        MIPS: devicetree: fix cpu interrupt controller node-names
        MIPS: VDSO: Build with `-fno-strict-aliasing'
        MIPS: Pistachio: Enable KASLR
        MIPS: lib: Mark intrinsics notrace
        MIPS: Fix 64-bit HTW configuration
        MIPS: Add 64-bit HTW fields
        MAINTAINERS: Add file patterns for mips device tree bindings
        MAINTAINERS: Add file patterns for mips brcm device tree bindings
        MIPS: Simplify DSP instruction encoding macros
        MIPS: Add missing tlbinvf/XPA microMIPS encodings
        MIPS: Fix little endian microMIPS MSA encodings
        MIPS: Add missing VZ accessor microMIPS encodings
        MIPS: Add inline asm encoding helpers
        MIPS: Spelling fix lets -> let's
        MIPS: VR41xx: Fix typo
        MIPS: oprofile: Fix typo
        MIPS: math-emu: Fix typo
        ...
      4029632c
    • Guenter Roeck's avatar
      fs: fix binfmt_aout.c build error · d66492bc
      Guenter Roeck authored
      Various builds (such as i386:allmodconfig) fail with
      
        fs/binfmt_aout.c:133:2: error: expected identifier or '(' before 'return'
        fs/binfmt_aout.c:134:1: error: expected identifier or '(' before '}' token
      
      [ Oops. My bad, I had stupidly thought that "allmodconfig" covered this
        on x86-64 too, but it obviously doesn't.  Egg on my face.  - Linus ]
      
      Fixes: 5d22fc25 ("mm: remove more IS_ERR_VALUE abuses")
      Signed-off-by: default avatarGuenter Roeck <linux@roeck-us.net>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      d66492bc
    • Linus Torvalds's avatar
      Merge branch 'hash' of git://ftp.sciencehorizons.net/linux · 7e0fb73c
      Linus Torvalds authored
      Pull string hash improvements from George Spelvin:
       "This series does several related things:
      
         - Makes the dcache hash (fs/namei.c) useful for general kernel use.
      
           (Thanks to Bruce for noticing the zero-length corner case)
      
         - Converts the string hashes in <linux/sunrpc/svcauth.h> to use the
           above.
      
         - Avoids 64-bit multiplies in hash_64() on 32-bit platforms.  Two
           32-bit multiplies will do well enough.
      
         - Rids the world of the bad hash multipliers in hash_32.
      
           This finishes the job started in commit 689de1d6 ("Minimal
           fix-up of bad hashing behavior of hash_64()")
      
           The vast majority of Linux architectures have hardware support for
           32x32-bit multiply and so derive no benefit from "simplified"
           multipliers.
      
           The few processors that do not (68000, h8/300 and some models of
           Microblaze) have arch-specific implementations added.  Those
           patches are last in the series.
      
         - Overhauls the dcache hash mixing.
      
           The patch in commit 0fed3ac8 ("namei: Improve hash mixing if
           CONFIG_DCACHE_WORD_ACCESS") was an off-the-cuff suggestion.
           Replaced with a much more careful design that's simultaneously
           faster and better.  (My own invention, as there was noting suitable
           in the literature I could find.  Comments welcome!)
      
         - Modify the hash_name() loop to skip the initial HASH_MIX().  This
           would let us salt the hash if we ever wanted to.
      
         - Sort out partial_name_hash().
      
           The hash function is declared as using a long state, even though
           it's truncated to 32 bits at the end and the extra internal state
           contributes nothing to the result.  And some callers do odd things:
      
            - fs/hfs/string.c only allocates 32 bits of state
            - fs/hfsplus/unicode.c uses it to hash 16-bit unicode symbols not bytes
      
         - Modify bytemask_from_count to handle inputs of 1..sizeof(long)
           rather than 0..sizeof(long)-1.  This would simplify users other
           than full_name_hash"
      
        Special thanks to Bruce Fields for testing and finding bugs in v1.  (I
        learned some humbling lessons about "obviously correct" code.)
      
        On the arch-specific front, the m68k assembly has been tested in a
        standalone test harness, I've been in contact with the Microblaze
        maintainers who mostly don't care, as the hardware multiplier is never
        omitted in real-world applications, and I haven't heard anything from
        the H8/300 world"
      
      * 'hash' of git://ftp.sciencehorizons.net/linux:
        h8300: Add <asm/hash.h>
        microblaze: Add <asm/hash.h>
        m68k: Add <asm/hash.h>
        <linux/hash.h>: Add support for architecture-specific functions
        fs/namei.c: Improve dcache hash function
        Eliminate bad hash multipliers from hash_32() and  hash_64()
        Change hash_64() return value to 32 bits
        <linux/sunrpc/svcauth.h>: Define hash_str() in terms of hashlen_string()
        fs/namei.c: Add hashlen_string() function
        Pull out string hash to <linux/stringhash.h>
      7e0fb73c
    • George Spelvin's avatar
      h8300: Add <asm/hash.h> · 4684fe95
      George Spelvin authored
      This will improve the performance of hash_32() and hash_64(), but due
      to complete lack of multi-bit shift instructions on H8, performance will
      still be bad in surrounding code.
      
      Designing H8-specific hash algorithms to work around that is a separate
      project.  (But if the maintainers would like to get in touch...)
      Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
      Cc: uclinux-h8-devel@lists.sourceforge.jp
      4684fe95
    • George Spelvin's avatar
      microblaze: Add <asm/hash.h> · 7b13277b
      George Spelvin authored
      Microblaze is an FPGA soft core that can be configured various ways.
      
      If it is configured without a multiplier, the standard __hash_32()
      will require a call to __mulsi3, which is a slow software loop.
      
      Instead, use a shift-and-add sequence for the constant multiply.
      GCC knows how to do this, but it's not as clever as some.
      Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Cc: Alistair Francis <alistair.francis@xilinx.com>
      Cc: Michal Simek <michal.simek@xilinx.com>
      7b13277b
    • George Spelvin's avatar
      m68k: Add <asm/hash.h> · 14c44b95
      George Spelvin authored
      This provides a multiply by constant GOLDEN_RATIO_32 = 0x61C88647
      for the original mc68000, which lacks a 32x32-bit multiply instruction.
      
      Yes, the amount of optimization effort put in is excessive. :-)
      
      Shift-add chain found by Yevgen Voronenko's Hcub algorithm at
      http://spiral.ece.cmu.edu/mcm/gen.htmlSigned-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Greg Ungerer <gerg@linux-m68k.org>
      Cc: Andreas Schwab <schwab@linux-m68k.org>
      Cc: Philippe De Muyter <phdm@macq.eu>
      Cc: linux-m68k@lists.linux-m68k.org
      14c44b95
    • George Spelvin's avatar
      <linux/hash.h>: Add support for architecture-specific functions · 468a9428
      George Spelvin authored
      This is just the infrastructure; there are no users yet.
      
      This is modelled on CONFIG_ARCH_RANDOM; a CONFIG_ symbol declares
      the existence of <asm/hash.h>.
      
      That file may define its own versions of various functions, and define
      HAVE_* symbols (no CONFIG_ prefix!) to suppress the generic ones.
      
      Included is a self-test (in lib/test_hash.c) that verifies the basics.
      It is NOT in general required that the arch-specific functions compute
      the same thing as the generic, but if a HAVE_* symbol is defined with
      the value 1, then equality is tested.
      Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Cc: Geert Uytterhoeven <geert@linux-m68k.org>
      Cc: Greg Ungerer <gerg@linux-m68k.org>
      Cc: Andreas Schwab <schwab@linux-m68k.org>
      Cc: Philippe De Muyter <phdm@macq.eu>
      Cc: linux-m68k@lists.linux-m68k.org
      Cc: Alistair Francis <alistai@xilinx.com>
      Cc: Michal Simek <michal.simek@xilinx.com>
      Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
      Cc: uclinux-h8-devel@lists.sourceforge.jp
      468a9428
    • George Spelvin's avatar
      fs/namei.c: Improve dcache hash function · 2a18da7a
      George Spelvin authored
      Patch 0fed3ac8 improved the hash mixing, but the function is slower
      than necessary; there's a 7-instruction dependency chain (10 on x86)
      each loop iteration.
      
      Word-at-a-time access is a very tight loop (which is good, because
      link_path_walk() is one of the hottest code paths in the entire kernel),
      and the hash mixing function must not have a longer latency to avoid
      slowing it down.
      
      There do not appear to be any published fast hash functions that:
      1) Operate on the input a word at a time, and
      2) Don't need to know the length of the input beforehand, and
      3) Have a single iterated mixing function, not needing conditional
         branches or unrolling to distinguish different loop iterations.
      
      One of the algorithms which comes closest is Yann Collet's xxHash, but
      that's two dependent multiplies per word, which is too much.
      
      The key insights in this design are:
      
      1) Barring expensive ops like multiplies, to diffuse one input bit
         across 64 bits of hash state takes at least log2(64) = 6 sequentially
         dependent instructions.  That is more cycles than we'd like.
      2) An operation like "hash ^= hash << 13" requires a second temporary
         register anyway, and on a 2-operand machine like x86, it's three
         instructions.
      3) A better use of a second register is to hold a two-word hash state.
         With careful design, no temporaries are needed at all, so it doesn't
         increase register pressure.  And this gets rid of register copying
         on 2-operand machines, so the code is smaller and faster.
      4) Using two words of state weakens the requirement for one-round mixing;
         we now have two rounds of mixing before cancellation is possible.
      5) A two-word hash state also allows operations on both halves to be
         done in parallel, so on a superscalar processor we get more mixing
         in fewer cycles.
      
      I ended up using a mixing function inspired by the ChaCha and Speck
      round functions.  It is 6 simple instructions and 3 cycles per iteration
      (assuming multiply by 9 can be done by an "lea" instruction):
      
      		x ^= *input++;
      	y ^= x;	x = ROL(x, K1);
      	x += y;	y = ROL(y, K2);
      	y *= 9;
      
      Not only is this reversible, two consecutive rounds are reversible:
      if you are given the initial and final states, but not the intermediate
      state, it is possible to compute both input words.  This means that at
      least 3 words of input are required to create a collision.
      
      (It also has the property, used by hash_name() to avoid a branch, that
      it hashes all-zero to all-zero.)
      
      The rotate constants K1 and K2 were found by experiment.  The search took
      a sample of random initial states (I used 1023) and considered the effect
      of flipping each of the 64 input bits on each of the 128 output bits two
      rounds later.  Each of the 8192 pairs can be considered a biased coin, and
      adding up the Shannon entropy of all of them produces a score.
      
      The best-scoring shifts also did well in other tests (flipping bits in y,
      trying 3 or 4 rounds of mixing, flipping all 64*63/2 pairs of input bits),
      so the choice was made with the additional constraint that the sum of the
      shifts is odd and not too close to the word size.
      
      The final state is then folded into a 32-bit hash value by a less carefully
      optimized multiply-based scheme.  This also has to be fast, as pathname
      components tend to be short (the most common case is one iteration!), but
      there's some room for latency, as there is a fair bit of intervening logic
      before the hash value is used for anything.
      
      (Performance verified with "bonnie++ -s 0 -n 1536:-2" on tmpfs.  I need
      a better benchmark; the numbers seem to show a slight dip in performance
      between 4.6.0 and this patch, but they're too noisy to quote.)
      
      Special thanks to Bruce fields for diligent testing which uncovered a
      nasty fencepost error in an earlier version of this patch.
      
      [checkpatch.pl formatting complaints noted and respectfully disagreed with.]
      Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Tested-by: default avatarJ. Bruce Fields <bfields@redhat.com>
      2a18da7a
    • George Spelvin's avatar
      Eliminate bad hash multipliers from hash_32() and hash_64() · ef703f49
      George Spelvin authored
      The "simplified" prime multipliers made very bad hash functions, so get rid
      of them.  This completes the work of 689de1d6.
      
      To avoid the inefficiency which was the motivation for the "simplified"
      multipliers, hash_64() on 32-bit systems is changed to use a different
      algorithm.  It makes two calls to hash_32() instead.
      
      drivers/media/usb/dvb-usb-v2/af9015.c uses the old GOLDEN_RATIO_PRIME_32
      for some horrible reason, so it inherits a copy of the old definition.
      Signed-off-by: default avatarGeorge Spelvin <linux@sciencehorizons.net>
      Cc: Antti Palosaari <crope@iki.fi>
      Cc: Mauro Carvalho Chehab <m.chehab@samsung.com>
      ef703f49