On function __find_get_block issue.

[asu]

Here is the file http://lxr.free-electrons.com/source/fs/buffer.c#L1354
Very strange here

52 */
1353 struct buffer_head *
1354 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1355 {
1356 struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1357
1358 if (bh == NULL) {
1359 /* __find_get_block_slow will mark the page accessed */
1360 bh = __find_get_block_slow(bdev, block);
1361 if (bh)
1362 bh_lru_install(bh);
1363 } else
1364 touch_buffer(bh);
1365
1366 return bh;
1367 }
1368 EXPORT_SYMBOL(__find_get_block);
struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
*bh is equalized without performing running look_bh_lru and after check for NULL pointer verry strange:

Bellow is content of perf report:
.............................

       │ mov %edx,%edx
       │ ↓ jmp 31
       │ 29:┌─→add $0x1,%ecx
       │ │ cmp $0x10,%ecx
       │ │↓ je 8e
       │ 31:│ mov %ecx,%r8d
       │ │ mov %gs:0x11080(,%r8,8),%rax
       │ │ test %rax,%rax
       │ │ mov %rax,%rbx
       │ │↑ je 29
       │ │ cmp 0x18(%rax),%rsi
100,00 │ └──jne 29
       │ cmp 0x30(%rax),%rdi
       │ ↑ jne 29
       │ cmp %rdx,0x20(%rax)
       │ ↑ jne 29
       │ test %ecx,%ecx
............................................

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-22-generic 4.4.0-22.40
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/pcmC0D0p: asu 3213 F...m pulseaudio
 /dev/snd/controlC0: asu 3213 F.... pulseaudio
CurrentDesktop: MATE
Date: Sat Jun 11 20:46:19 2016
InstallationDate: Installed on 2016-04-29 (43 days ago)
InstallationMedia: Ubuntu-Studio 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
IwConfig:
 lo no wireless extensions.

 enp1s0 no wireless extensions.
MachineType: Olidata S.p.A. ALABAMA
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-22-generic root=/dev/mapper/192--168--0--108--vg-root ro
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-22-generic N/A
 linux-backports-modules-4.4.0-22-generic N/A
 linux-firmware 1.157
RfKill:

SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/08/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: S0101
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: To be filled by O.E.M.
dmi.board.vendor: To be filled by O.E.M.
dmi.board.version: To be filled by O.E.M.
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrS0101:bd07/08/2008:svnOlidataS.p.A.:pnALABAMA:pvrToBeFilledByO.E.M.:rvnTobefilledbyO.E.M.:rnTobefilledbyO.E.M.:rvrTobefilledbyO.E.M.:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: ALABAMA
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: Olidata S.p.A.

[Brad Figg (brad-figg)]

This change was made by a bot.

[Joseph Salisbury (jsalisbury)]

This issue appears to be an upstream bug. Would it be possible for you to open an upstream bug report[0]? That will allow the upstream Developers to examine the issue, and may provide a quicker resolution to the bug.

Please follow the instructions on the wiki page[0]. The first step is to email the appropriate mailing list. If no response is received, then a bug may be opened on bugzilla.kernel.org.

Once this bug is reported upstream, please add the tag: 'kernel-bug-reported-upstream'.

[0] https://wiki.ubuntu.com/Bugs/Upstream/kernel