This adds address space operations for data.

- F2FS supports readpages(), writepages(), and direct_IO().

- Because of out-of-place writes, f2fs_direct_IO() does not write data in place.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds memory operations and file/file_inode operations.

- F2FS supports fallocate(), mmap(), fsync(), and basic ioctl().
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds specific functions not only to manage dirty/free segments, SIT pages,
a cache for SIT entries, and summary entries, but also to allocate free blocks
and write three types of pages: data, node, and meta.

- F2FS maintains three types of bitmaps in memory, which indicate free, prefree,
  and dirty segments respectively.

- The key information of an SIT entry consists of a segment number, the number
  of valid blocks in the segment, a bitmap to identify there-in valid or invalid
  blocks.

- An SIT page is composed of a certain range of SIT entries, which is maintained
  by the address space of meta_inode.

- To cache SIT entries, a simple array is used. The index for the array is the
  segment number.

- A summary entry for data contains the parent node information. A summary entry
  for node contains its node offset from the inode.

- F2FS manages information about six active logs and those summary entries in
  memory. Whenever one of them is changed, its summary entries are flushed to
  its SIT page maintained by the address space of meta_inode.

- This patch adds a default block allocation function which supports heap-based
  allocation policy.

- This patch adds core functions to write data, node, and meta pages. Since LFS
  basically produces a series of sequential writes, F2FS merges sequential bios
  with a single one as much as possible to reduce the IO scheduling overhead.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds specific functions to manage NAT pages, a cache for NAT entries, free
nids, direct/indirect node blocks for indexing data, and address space for node
pages.

- The key information of an NAT entry consists of a node id and a block address.

- An NAT page is composed of block addresses covered by a certain range of NAT
  entries, which is maintained by the address space of meta_inode.

- A radix tree structure is used to cache NAT entries. The index for the tree
  is a node id.

- When there is no free nid, F2FS should scan NAT entries to find new one. In
  order to avoid scanning frequently, F2FS manages a list containing a number of
  free nids in memory. Only when free nids in the list are exhausted, scanning
  process, build_free_nids(), is triggered.

- F2FS has direct and indirect node blocks for indexing data. This patch adds
  fuctions related to the node block management such as getting, allocating, and
  truncating node blocks to index data.

- In order to cache node blocks in memory, F2FS has a node_inode with an address
  space for node pages. This patch also adds the address space operations for
  node_inode.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds functions required by the checkpoint operations.

Basically, f2fs adopts a roll-back model with checkpoint blocks written in the
CP area. The checkpoint procedure includes as follows.

- write_checkpoint()
1. block_operations() freezes VFS calls.
2. submit cached bios.
3. flush_nat_entries() writes NAT pages updated by dirty NAT entries.
4. flush_sit_entries() writes SIT pages updated by dirty SIT entries.
5. do_checkpoint() writes,
  - checkpoint block (#0)
  - orphan inode blocks
  - summary blocks made by active logs
  - checkpoint block (copy of #0)
6. unblock_opeations()

In order to provide an address space for meta pages, f2fs_sb_info has a special
inode, namely meta_inode. This patch also adds the address space operations for
meta_inode.
Signed-off-by: Chul Lee <chur.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds the implementation of superblock operations for f2fs, which includes
- init_f2fs_fs/exit_f2fs_fs
- f2fs_mount
- super_operations of f2fs
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds the following major in-memory structures in f2fs.

- f2fs_sb_info:
  contains f2fs-specific information, two special inode pointers for node and
  meta address spaces, and orphan inode management.

- f2fs_inode_info:
  contains vfs_inode and other fs-specific information.

- f2fs_nm_info:
  contains node manager information such as NAT entry cache, free nid list,
  and NAT page management.

- f2fs_node_info:
  represents a node as node id, inode number, block address, and its version.

- f2fs_sm_info:
  contains segment manager information such as SIT entry cache, free segment
  map, current active logs, dirty segment management, and segment utilization.
  The specific structures are sit_info, free_segmap_info, dirty_seglist_info,
  curseg_info.

In addition, add F2FS_SUPER_MAGIC in magic.h.
Signed-off-by: Chul Lee <chur.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds a header file describing the on-disk layout of f2fs.
Signed-off-by: Changman Lee <cm224.lee@samsung.com>
Signed-off-by: Chul Lee <chur.lee@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

This adds a document describing the mount options, proc entries, usage, and
design of Flash-Friendly File System, namely F2FS.
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

The matrix-keymap module is currently lacking a proper module license,
add one so we don't have this module tainting the entire kernel.  This
issue has been present since commit 1932811f ("Input: matrix-keymap
- uninline and prepare for device tree support")
Signed-off-by: Florian Fainelli <florian@openwrt.org>
CC: stable@vger.kernel.org # v3.5+
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull networking fixes from David Miller:

 1) Netlink socket dumping had several missing verifications and checks.

    In particular, address comparisons in the request byte code
    interpreter could access past the end of the address in the
    inet_request_sock.

    Also, address family and address prefix lengths were not validated
    properly at all.

    This means arbitrary applications can read past the end of certain
    kernel data structures.

    Fixes from Neal Cardwell.

 2) ip_check_defrag() operates in contexts where we're in the process
    of, or about to, input the packet into the real protocols
    (specifically macvlan and AF_PACKET snooping).

    Unfortunately, it does a pskb_may_pull() which can modify the
    backing packet data which is not legal if the SKB is shared.  It
    very much can be shared in this context.

    Deal with the possibility that the SKB is segmented by using
    skb_copy_bits().

    Fix from Johannes Berg based upon a report by Eric Leblond.

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net:
  ipv4: ip_check_defrag must not modify skb before unsharing
  inet_diag: validate port comparison byte code to prevent unsafe reads
  inet_diag: avoid unsafe and nonsensical prefix matches in inet_diag_bc_run()
  inet_diag: validate byte code to prevent oops in inet_diag_bc_run()
  inet_diag: fix oops for IPv4 AF_INET6 TCP SYN-RECV state

This reverts commits a5091539 and
d7c3b937.

This is a revert of a revert of a revert.  In addition, it reverts the
even older i915 change to stop using the __GFP_NO_KSWAPD flag due to the
original commits in linux-next.

It turns out that the original patch really was bogus, and that the
original revert was the correct thing to do after all.  We thought we
had fixed the problem, and then reverted the revert, but the problem
really is fundamental: waking up kswapd simply isn't the right thing to
do, and direct reclaim sometimes simply _is_ the right thing to do.

When certain allocations fail, we simply should try some direct reclaim,
and if that fails, fail the allocation.  That's the right thing to do
for THP allocations, which can easily fail, and the GPU allocations want
to do that too.

So starting kswapd is sometimes simply wrong, and removing the flag that
said "don't start kswapd" was a mistake.  Let's hope we never revisit
this mistake again - and certainly not this many times ;)
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

ip_check_defrag() might be called from af_packet within the
RX path where shared SKBs are used, so it must not modify
the input SKB before it has unshared it for defragmentation.
Use skb_copy_bits() to get the IP header and only pull in
everything later.

The same is true for the other caller in macvlan as it is
called from dev->rx_handler which can also get a shared SKB.
Reported-by: Eric Leblond <eric@regit.org>
Cc: stable@vger.kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

This reverts commit 782fd304.

We are going to reinstate the __GFP_NO_KSWAPD flag that has been
removed, the removal reverted, and then removed again.  Making this
commit a pointless fixup for a problem that was caused by the removal of
__GFP_NO_KSWAPD flag.

The thing is, we really don't want to wake up kswapd for THP allocations
(because they fail quite commonly under any kind of memory pressure,
including when there is tons of memory free), and these patches were
just trying to fix up the underlying bug: the original removal of
__GFP_NO_KSWAPD in commit c6543459 ("mm: remove __GFP_NO_KSWAPD")
was simply bogus.
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Add logic to verify that a port comparison byte code operation
actually has the second inet_diag_bc_op from which we read the port
for such operations.

Previously the code blindly referenced op[1] without first checking
whether a second inet_diag_bc_op struct could fit there. So a
malicious user could make the kernel read 4 bytes beyond the end of
the bytecode array by claiming to have a whole port comparison byte
code (2 inet_diag_bc_op structs) when in fact the bytecode was not
long enough to hold both.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add logic to check the address family of the user-supplied conditional
and the address family of the connection entry. We now do not do
prefix matching of addresses from different address families (AF_INET
vs AF_INET6), except for the previously existing support for having an
IPv4 prefix match an IPv4-mapped IPv6 address (which this commit
maintains as-is).

This change is needed for two reasons:

(1) The addresses are different lengths, so comparing a 128-bit IPv6
prefix match condition to a 32-bit IPv4 connection address can cause
us to unwittingly walk off the end of the IPv4 address and read
garbage or oops.

(2) The IPv4 and IPv6 address spaces are semantically distinct, so a
simple bit-wise comparison of the prefixes is not meaningful, and
would lead to bogus results (except for the IPv4-mapped IPv6 case,
which this commit maintains).
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Add logic to validate INET_DIAG_BC_S_COND and INET_DIAG_BC_D_COND
operations.

Previously we did not validate the inet_diag_hostcond, address family,
address length, and prefix length. So a malicious user could make the
kernel read beyond the end of the bytecode array by claiming to have a
whole inet_diag_hostcond when the bytecode was not long enough to
contain a whole inet_diag_hostcond of the given address family. Or
they could make the kernel read up to about 27 bytes beyond the end of
a connection address by passing a prefix length that exceeded the
length of addresses of the given family.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Fix inet_diag to be aware of the fact that AF_INET6 TCP connections
instantiated for IPv4 traffic and in the SYN-RECV state were actually
created with inet_reqsk_alloc(), instead of inet6_reqsk_alloc(). This
means that for such connections inet6_rsk(req) returns a pointer to a
random spot in memory up to roughly 64KB beyond the end of the
request_sock.

With this bug, for a server using AF_INET6 TCP sockets and serving
IPv4 traffic, an inet_diag user like `ss state SYN-RECV` would lead to
inet_diag_fill_req() causing an oops or the export to user space of 16
bytes of kernel memory as a garbage IPv6 address, depending on where
the garbage inet6_rsk(req) pointed.
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

commit c702418f ("mm: vmscan: do not keep kswapd looping forever due
to individual uncompactable zones") removed zone watermark checks from
the compaction code in kswapd but left in the zone congestion clearing,
which now happens unconditionally on higher order reclaim.

This messes up the reclaim throttling logic for zones with
dirty/writeback pages, where zones should only lose their congestion
status when their watermarks have been restored.

Remove the clearing from the zone compaction section entirely.  The
preliminary zone check and the reclaim loop in kswapd will clear it if
the zone is considered balanced.
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

The direct-IO write path already had the i_size checks in mm/filemap.c,
but it turns out the read path did not, and removing the block size
checks in fs/block_dev.c (commit bbec0270: "blkdev_max_block: make
private to fs/buffer.c") removed the magic "shrink IO to past the end of
the device" code there.

Fix it by truncating the IO to the size of the block device, like the
write path already does.

NOTE! I suspect the write path would be *much* better off doing it this
way in fs/block_dev.c, rather than hidden deep in mm/filemap.c.  The
mm/filemap.c code is extremely hard to follow, and has various
conditionals on the target being a block device (ie the flag passed in
to 'generic_write_checks()', along with a conditional update of the
inode timestamp etc).

It is also quite possible that we should treat this whole block device
size as a "s_maxbytes" issue, and try to make the logic even more
generic.  However, in the meantime this is the fairly minimal targeted
fix.

Noted by Milan Broz thanks to a regression test for the cryptsetup
reencrypt tool.
Reported-and-tested-by: Milan Broz <mbroz@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull networking fixes from David Miller:
 "Two stragglers:

   1) The new code that adds new flushing semantics to GRO can cause SKB
      pointer list corruption, manage the lists differently to avoid the
      OOPS.  Fix from Eric Dumazet.

   2) When TCP fast open does a retransmit of data in a SYN-ACK or
      similar, we update retransmit state that we shouldn't triggering a
      WARN_ON later.  Fix from Yuchung Cheng."

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net:
  net: gro: fix possible panic in skb_gro_receive()
  tcp: bug fix Fast Open client retransmission

commit 2e71a6f8 (net: gro: selective flush of packets) added
a bug for skbs using frag_list. This part of the GRO stack is rarely
used, as it needs skb not using a page fragment for their skb->head.

Most drivers do use a page fragment, but some of them use GFP_KERNEL
allocations for the initial fill of their RX ring buffer.

napi_gro_flush() overwrite skb->prev that was used for these skb to
point to the last skb in frag_list.

Fix this using a separate field in struct napi_gro_cb to point to the
last fragment.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

If SYN-ACK partially acks SYN-data, the client retransmits the
remaining data by tcp_retransmit_skb(). This increments lost recovery
state variables like tp->retrans_out in Open state. If loss recovery
happens before the retransmission is acked, it triggers the WARN_ON
check in tcp_fastretrans_alert(). For example: the client sends
SYN-data, gets SYN-ACK acking only ISN, retransmits data, sends
another 4 data packets and get 3 dupacks.

Since the retransmission is not caused by network drop it should not
update the recovery state variables. Further the server may return a
smaller MSS than the cached MSS used for SYN-data, so the retranmission
needs a loop. Otherwise some data will not be retransmitted until timeout
or other loss recovery events.
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Pull MMC fixes from Chris Ball:
 "Two small regression fixes:

   - sdhci-s3c: Fix runtime PM regression against 3.7-rc1
   - sh-mmcif: Fix oops against 3.6"

* tag 'mmc-fixes-for-3.7' of git://git.kernel.org/pub/scm/linux/kernel/git/cjb/mmc:
  mmc: sh-mmcif: avoid oops on spurious interrupts (second try)
  Revert misapplied "mmc: sh-mmcif: avoid oops on spurious interrupts"
  mmc: sdhci-s3c: fix missing clock for gpio card-detect

This fixes a regression in 3.7-rc, which has since gone into stable.

Commit 00442ad0 ("mempolicy: fix a memory corruption by refcount
imbalance in alloc_pages_vma()") changed get_vma_policy() to raise the
refcount on a shmem shared mempolicy; whereas shmem_alloc_page() went
on expecting alloc_page_vma() to drop the refcount it had acquired.
This deserves a rework: but for now fix the leak in shmem_alloc_page().

Hugh: shmem_swapin() did not need a fix, but surely it's clearer to use
the same refcounting there as in shmem_alloc_page(), delete its onstack
mempolicy, and the strange mpol_cond_copy() and __mpol_cond_copy() -
those were invented to let swapin_readahead() make an unknown number of
calls to alloc_pages_vma() with one mempolicy; but since 00442ad0,
alloc_pages_vma() has kept refcount in balance, so now no problem.
Reported-and-tested-by: Tommi Rantala <tt.rantala@gmail.com>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

When a zone meets its high watermark and is compactable in case of
higher order allocations, it contributes to the percentage of the node's
memory that is considered balanced.

This requirement, that a node be only partially balanced, came about
when kswapd was desparately trying to balance tiny zones when all bigger
zones in the node had plenty of free memory.  Arguably, the same should
apply to compaction: if a significant part of the node is balanced
enough to run compaction, do not get hung up on that tiny zone that
might never get in shape.

When the compaction logic in kswapd is reached, we know that at least
25% of the node's memory is balanced properly for compaction (see
zone_balanced and pgdat_balanced).  Remove the individual zone checks
that restart the kswapd cycle.

Otherwise, we may observe more endless looping in kswapd where the
compaction code loops back to reclaim because of a single zone and
reclaim does nothing because the node is considered balanced overall.

See for example

  https://bugzilla.redhat.com/show_bug.cgi?id=866988Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-and-tested-by: Thorsten Leemhuis <fedora@leemhuis.info>
Reported-by: Jiri Slaby <jslaby@suse.cz>
Tested-by: John Ellson <john.ellson@comcast.net>
Tested-by: Zdenek Kabelac <zkabelac@redhat.com>
Tested-by: Bruno Wolff III <bruno@wolff.to>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Commit 0bf380bc ("mm: compaction: check pfn_valid when entering a
new MAX_ORDER_NR_PAGES block during isolation for migration") added a
check for pfn_valid() when isolating pages for migration as the scanner
does not necessarily start pageblock-aligned.

Since commit c89511ab ("mm: compaction: Restart compaction from near
where it left off"), the free scanner has the same problem.  This patch
makes sure that the pfn range passed to isolate_freepages_block() is
within the same block so that pfn_valid() checks are unnecessary.

In answer to Henrik's wondering why others have not reported this:
reproducing this requires a large enough hole with the right aligment to
have compaction walk into a PFN range with no memmap.  Size and
alignment depends in the memory model - 4M for FLATMEM and 128M for
SPARSEMEM on x86.  It needs a "lucky" machine.
Reported-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

On some systems, e.g., kzm9g, MMCIF interfaces can produce spurious
interrupts without any active request. To prevent the Oops, that results
in such cases, don't dereference the mmc request pointer until we make
sure, that we are indeed processing such a request.
Reported-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Cc: stable@vger.kernel.org
Signed-off-by: Chris Ball <cjb@laptop.org>

This reverts commit 8464dd52, which was a misapplied debugging
version of the patch, not the final patch itself.
Signed-off-by: Chris Ball <cjb@laptop.org>
Cc: stable@vger.kernel.org

2abeb5c5 ("Add clk_(enable/disable) in runtime suspend/resume")
added the capability to stop the clocks when the device is runtime
suspended, but forgot to handle the case of the card-detect using
an external gpio.

Therefore in the case that runtime-pm is enabled, start the io-clock
when a card is inserted and stop it again once it is removed.
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

Pull MIPS fixes from Ralf Baechle:
 "These are the fixes for the N32 syscall bugs found by Al, an
  extraneous break that broke detection for R3000 and R3081 processors,
  an endless loop processing signals for kernel task (x86 received the
  same fix a while ago) and a fix for transparent huge page which took
  ages to track down because it was so hard to come up with a workable
  test case."

* 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus:
  MIPS: Fix endless loop when processing signals for kernel tasks
  MIPS: R3000/R3081: Fix CPU detection.
  MIPS: N32: Fix signalfd4 syscall entry point
  MIPS: N32: Fix preadv(2) and pwritev(2) entry points.
  MIPS: Avoid mcheck by flushing page range in huge_ptep_set_access_flags()

Pull build fix from Rusty Russell:
 "Tim Gardner <tim.gardner@canonical.com> writes:
  > It is $(obj)/oid_registry.o that is dependent on $(obj)/oid_registry_data.c.
  > The object file cannot be built until $(obj)/oid_registry_data.c has been
  > generated.
  >
  > A periodic and hard to reproduce parallel build failure is due to
  > this incorrect lib/Makefile dependency. The compile error is completely
  > disingenuous.
  >
  >   GEN     lib/oid_registry_data.c
  > Compiling 49 OIDs
  >   CC      lib/oid_registry.o
  > gcc: error: lib/oid_registry.c: No such file or directory
  > gcc: fatal error: no input files
  > compilation terminated.
  > make[3]: *** [lib/oid_registry.o] Error 4

  I can't reproduce it either.  It's completely weird; nothing ever
  removes lib/oid_registry.c, so either gcc is giving the wrong message
  or it's a weird fs with a very odd race.

  But your version is definitely more correct than the previous one,
  so..."

* 'more-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux:
  lib/Makefile: Fix oid_registry build dependency

Pull module signing fixes from Rusty Russell:
 "David gave me these a month ago, during my git workflow churn :("

* 'fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux:
  ASN.1: Fix an indefinite length skip error
  MODSIGN: Don't use enum-type bitfields in module signature info block

Pull watchdog fix from Thomas Gleixner:
 "Trivial CPU hotplug regression fix for the watchdog code"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  watchdog: Fix CPU hotplug regression

It is $(obj)/oid_registry.o that is dependent on $(obj)/oid_registry_data.c.
The object file cannot be built until $(obj)/oid_registry_data.c has been
generated.

A periodic and hard to reproduce parallel build failure is due to
this incorrect lib/Makefile dependency. The compile error is completely
disingenuous.

  GEN     lib/oid_registry_data.c
Compiling 49 OIDs
  CC      lib/oid_registry.o
gcc: error: lib/oid_registry.c: No such file or directory
gcc: fatal error: no input files
compilation terminated.
make[3]: *** [lib/oid_registry.o] Error 4

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

The problem occurs [1] when a kernel-mode task returns from a system
call with a pending signal.

A real-life scenario is a child of 'khelper' returning from a failed
kernel_execve() in ____call_usermodehelper() [ kernel/kmod.c ].
kernel_execve() fails due to a pending SIGKILL, which is the result of
"kill -9 -1" (at least, busybox's init does it upon reboot).

The loop is as follows:

* syscall_exit_work:
 - work_pending:            // start_of_the_loop
 - work_notifysig:
   - do_notify_resume()
     - do_signal()
       - if (!user_mode(regs)) return;
 - resume_userspace         // TIF_SIGPENDING is still set
 - work_pending             // so we call work_pending => goto
                            // start_of_the_loop

More information can be found in another LKML thread:
http://www.serverphorums.com/read.php?12,457826

[1] The problem was also reproduced on !CONFIG_VM86 x86, and the
following fix was accepted.

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=29a2e2836ff9ea65a603c89df217f4198973a74fSigned-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3571/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

Broken since e05ea74fc56f347f872ef9946d27c53e8bf20864 (lmo) rsp.
cea7e2df (kernel.org) [MIPS: Sort out CPU
type to name translation.]  These CPUs are no longer very popular to say
the least ...
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Reported-by: Murphy McCauley <murphy.mccauley@gmail.com>

This needs to use the compat entry point or it's going to fail on big
endian systems.

Noticed by Al Viro.
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

READ is zero so the "rw & READ" test is always false.  The intended test
was "((rw & RW_MASK) == READ)".
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>