Don't burden the common block code with with specifics of the libata DMA
draining mechanism.  Instead move most of the code to the scsi midlayer.

That also means the nr_phys_segments adjustments in the blk-mq fast path
can go away entirely, given that SCSI never looks at nr_phys_segments
after mapping the request to a scatterlist.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

scsi_init_io is the only caller of scsi_init_sgtable.  Merge the two
function to make upcoming changes a little easier.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

To be able to move some of the special purpose hacks in blk_rq_map_sg
into the callers we need a variant that returns the last mapped
S/G list element to the caller.  Add that variant as __blk_rq_map_sg
and make blk_rq_map_sg a trivial inline wrapper around it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

The RQF_COPY_USER is set for bio where the passthrough request mapping
helpers decided that bounce buffering is required.  It is then used to
pad scatterlist for drivers that required it.  But given that
non-passthrough requests are per definition aligned, and directly mapped
pass-through request must be aligned it is not actually required at all.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

invalidate_partition and bdev_unhash_inode are always paired, and
invalidate_partition already does an icache lookup for the block device
inode.  Piggy back on that to remove the inode from the hash.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

invalidate_partition is only used in genhd.c, so mark it static.  Also
drop the return value given that is is always ignored.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We just checked a little above that the block device for the partition
im busy.  That implies no file system is mounted, and thus the only
thing in fsync_bdev that actually is used is sync_blockdev.  Just call
sync_blockdev directly.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Given that the device must not be busy, most of the calls from
invalidate_partition that are related to file system metadata are
guranteed to not happen.  Just open code the calls to sync_blockdev
and invalidate_bdev instead.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Use the blk_drop_partitions function instead of messing around with
ioctls that get kernel pointers.  For this blk_drop_partitions needs
to be exported, which it normally shouldn't - make an exception for
s390 only.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

The gendisk can be trivially deducted from the block_device.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

The function has a single caller, so just open code it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Move hd_ref_init out of line as there it isn't anywhere near a fast path,
and rename the rcu ref freeing callbacks to be more descriptive.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

All callers have the hd_struct at hand, so pass it instead of performing
another lookup.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Split each sub-command out into a separate helper, and move those helpers
to block/partitions/core.c instead of having a lot of partition
manipulation logic open coded in block/ioctl.c.

Signed-off-by: Christoph Hellwig <hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This reverts commit 7e70aa78.

Now that we have the patches ("blk-mq: In blk_mq_dispatch_rq_list()
"no budget" is a reason to kick") and ("blk-mq: Rerun dispatching in
the case of budget contention") we should no longer need the fix in
the SCSI code.  Revert it, resolving conflicts with other patches that
have touched this code.

With this revert (and the two new patches) I can run the script that
was in commit 7e70aa78 ("scsi: core: run queue if SCSI device
queue isn't ready and queue is idle") in a loop with no failure.  If I
do this revert without the two new patches I can easily get a failure.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

If ever a thread running blk-mq code tries to get budget and fails it
immediately stops doing work and assumes that whenever budget is freed
up that queues will be kicked and whatever work the thread was trying
to do will be tried again.

One path where budget is freed and queues are kicked in the normal
case can be seen in scsi_finish_command().  Specifically:
- scsi_finish_command()
  - scsi_device_unbusy()
    - # Decrement "device_busy", AKA release budget
  - scsi_io_completion()
    - scsi_end_request()
      - blk_mq_run_hw_queues()

The above is all well and good.  The problem comes up when a thread
claims the budget but then releases it without actually dispatching
any work.  Since we didn't schedule any work we'll never run the path
of finishing work / kicking the queues.

This isn't often actually a problem which is why this issue has
existed for a while and nobody noticed.  Specifically we only get into
this situation when we unexpectedly found that we weren't going to do
any work.  Code that later receives new work kicks the queues.  All
good, right?

The problem shows up, however, if timing is just wrong and we hit a
race.  To see this race let's think about the case where we only have
a budget of 1 (only one thread can hold budget).  Now imagine that a
thread got budget and then decided not to dispatch work.  It's about
to call put_budget() but then the thread gets context switched out for
a long, long time.  While in this state, any and all kicks of the
queue (like the when we received new work) will be no-ops because
nobody can get budget.  Finally the thread holding budget gets to run
again and returns.  All the normal kicks will have been no-ops and we
have an I/O stall.

As you can see from the above, you need just the right timing to see
the race.  To start with, the only case it happens if we thought we
had work, actually managed to get the budget, but then actually didn't
have work.  That's pretty rare to start with.  Even then, there's
usually a very small amount of time between realizing that there's no
work and putting the budget.  During this small amount of time new
work has to come in and the queue kick has to make it all the way to
trying to get the budget and fail.  It's pretty unlikely.

One case where this could have failed is illustrated by an example of
threads running blk_mq_do_dispatch_sched():

* Threads A and B both run has_work() at the same time with the same
  "hctx".  Imagine has_work() is exact.  There's no lock, so it's OK
  if Thread A and B both get back true.
* Thread B gets interrupted for a long time right after it decides
  that there is work.  Maybe its CPU gets an interrupt and the
  interrupt handler is slow.
* Thread A runs, get budget, dispatches work.
* Thread A's work finishes and budget is released.
* Thread B finally runs again and gets budget.
* Since Thread A already took care of the work and no new work has
  come in, Thread B will get NULL from dispatch_request().  I believe
  this is specifically why dispatch_request() is allowed to return
  NULL in the first place if has_work() must be exact.
* Thread B will now be holding the budget and is about to call
  put_budget(), but hasn't called it yet.
* Thread B gets interrupted for a long time (again).  Dang interrupts.
* Now Thread C (maybe with a different "hctx" but the same queue)
  comes along and runs blk_mq_do_dispatch_sched().
* Thread C won't do anything because it can't get budget.
* Finally Thread B will run again and put the budget without kicking
  any queues.

Even though the example above is with blk_mq_do_dispatch_sched() I
believe the race is possible any time someone is holding budget but
doesn't do work.

Unfortunately, the unlikely has become more likely if you happen to be
using the BFQ I/O scheduler.  BFQ, by design, sometimes returns "true"
for has_work() but then NULL for dispatch_request() and stays in this
state for a while (currently up to 9 ms).  Suddenly you only need one
race to hit, not two races in a row.  With my current setup this is
easy to reproduce in reboot tests and traces have actually shown that
we hit a race similar to the one described above.

Note that we only need to fix blk_mq_do_dispatch_sched() and
blk_mq_do_dispatch_ctx() and not the other places that put budget.  In
other cases we know that we have work to do on at least one "hctx" and
code already exists to kick that "hctx"'s queue.  When that work
finally finishes all the queues will be kicked using the normal flow.

One last note is that (at least in the SCSI case) budget is shared by
all "hctx"s that have the same queue.  Thus we need to make sure to
kick the whole queue, not just re-run dispatching on a single "hctx".
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We have:
* blk_mq_run_hw_queue()
* blk_mq_delay_run_hw_queue()
* blk_mq_run_hw_queues()

...but not blk_mq_delay_run_hw_queues(), presumably because nobody
needed it before now.  Since we need it for a later patch in this
series, add it.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

In blk_mq_dispatch_rq_list(), if blk_mq_sched_needs_restart() returns
true and the driver returns BLK_STS_RESOURCE then we'll kick the
queue.  However, there's another case where we might need to kick it.
If we were unable to get budget we can be in much the same state as
when the driver returns BLK_STS_RESOURCE, so we should treat it the
same.

It should be noted that even if we add a whole bunch of extra kicking
to the queue in other patches this patch is still important.
Specifically any kicking that happened before we re-spliced leftover
requests into 'hctx->dispatch' wouldn't have found any work, so we
really need to make sure we kick ourselves after we've done the
splicing.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

When remapping a mapping where a portion of a VMA is remapped
into another portion of the VMA it can cause the VMA to become
split. During the copy_vma operation the VMA can actually
be remerged if it's an anonymous VMA whose pages have not yet
been faulted. This isn't normally a problem because at the end
of the remap the original portion is unmapped causing it to
become split again.

However, MREMAP_DONTUNMAP leaves that original portion in place which
means that the VMA which was split and then remerged is not actually
split at the end of the mremap. This patch fixes a bug where
we don't detect that the VMAs got remerged and we end up
putting back VM_ACCOUNT on the next mapping which is completely
unreleated. When that next mapping is unmapped it results in
incorrectly unaccounting for the memory which was never accounted,
and eventually we will underflow on the memory comittment.

There is also another issue which is similar, we're currently
accouting for the number of pages in the new_vma but that's wrong.
We need to account for the length of the remap operation as that's
all that is being added. If there was a mapping already at that
location its comittment would have been adjusted as part of
the munmap at the start of the mremap.

A really simple repro can be seen in:
https://gist.github.com/bgaff/e101ce99da7d9a8c60acc641d07f312c

Fixes: e346b381 ("mm/mremap: add MREMAP_DONTUNMAP to mremap()")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Brian Geffon <bgeffon@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull clk fixes from Stephen Boyd:
 "Two build fixes for a couple clk drivers and a fix for the Unisoc
  serial clk where we want to keep it on for earlycon"

* tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux:
  clk: sprd: don't gate uart console clock
  clk: mmp2: fix link error without mmp2
  clk: asm9260: fix __clk_hw_register_fixed_rate_with_accuracy typo

Pull x86 and objtool fixes from Thomas Gleixner:
 "A set of fixes for x86 and objtool:

  objtool:

   - Ignore the double UD2 which is emitted in BUG() when
     CONFIG_UBSAN_TRAP is enabled.

   - Support clang non-section symbols in objtool ORC dump

   - Fix switch table detection in .text.unlikely

   - Make the BP scratch register warning more robust.

  x86:

   - Increase microcode maximum patch size for AMD to cope with new CPUs
     which have a larger patch size.

   - Fix a crash in the resource control filesystem when the removal of
     the default resource group is attempted.

   - Preserve Code and Data Prioritization enabled state accross CPU
     hotplug.

   - Update split lock cpu matching to use the new X86_MATCH macros.

   - Change the split lock enumeration as Intel finaly decided that the
     IA32_CORE_CAPABILITIES bits are not architectural contrary to what
     the SDM claims. !@#%$^!

   - Add Tremont CPU models to the split lock detection cpu match.

   - Add a missing static attribute to make sparse happy"

* tag 'x86-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/split_lock: Add Tremont family CPU models
  x86/split_lock: Bits in IA32_CORE_CAPABILITIES are not architectural
  x86/resctrl: Preserve CDP enable over CPU hotplug
  x86/resctrl: Fix invalid attempt at removing the default resource group
  x86/split_lock: Update to use X86_MATCH_INTEL_FAM6_MODEL()
  x86/umip: Make umip_insns static
  x86/microcode/AMD: Increase microcode PATCH_MAX_SIZE
  objtool: Make BP scratch register warning more robust
  objtool: Fix switch table detection in .text.unlikely
  objtool: Support Clang non-section symbols in ORC generation
  objtool: Support Clang non-section symbols in ORC dump
  objtool: Fix CONFIG_UBSAN_TRAP unreachable warnings

Pull time namespace fix from Thomas Gleixner:
 "An update for the proc interface of time namespaces: Use symbolic
  names instead of clockid numbers. The usability nuisance of numbers
  was noticed by Michael when polishing the man page"

* tag 'timers-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  proc, time/namespace: Show clock symbolic names in /proc/pid/timens_offsets

Pull perf tooling fixes and updates from Thomas Gleixner:

 - Fix the header line of perf stat output for '--metric-only --per-socket'

 - Fix the python build with clang

 - The usual tools UAPI header synchronization

* tag 'perf-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tools headers: Synchronize linux/bits.h with the kernel sources
  tools headers: Adopt verbatim copy of compiletime_assert() from kernel sources
  tools headers: Update x86's syscall_64.tbl with the kernel sources
  tools headers UAPI: Sync drm/i915_drm.h with the kernel sources
  tools headers UAPI: Update tools's copy of drm.h headers
  tools headers kvm: Sync linux/kvm.h with the kernel sources
  tools headers UAPI: Sync linux/fscrypt.h with the kernel sources
  tools include UAPI: Sync linux/vhost.h with the kernel sources
  tools arch x86: Sync asm/cpufeatures.h with the kernel sources
  tools headers UAPI: Sync linux/mman.h with the kernel
  tools headers UAPI: Sync sched.h with the kernel
  tools headers: Update linux/vdso.h and grab a copy of vdso/const.h
  perf stat: Fix no metric header if --per-socket and --metric-only set
  perf python: Check if clang supports -fno-semantic-interposition
  tools arch x86: Sync the msr-index.h copy with the kernel sources

Pull irq fixes from Thomas Gleixner:
 "A set of fixes/updates for the interrupt subsystem:

   - Remove setup_irq() and remove_irq(). All users have been converted
     so remove them before new users surface.

   - A set of bugfixes for various interrupt chip drivers

   - Add a few missing static attributes to address sparse warnings"

* tag 'irq-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  irqchip/irq-bcm7038-l1: Make bcm7038_l1_of_init() static
  irqchip/irq-mvebu-icu: Make legacy_bindings static
  irqchip/meson-gpio: Fix HARDIRQ-safe -> HARDIRQ-unsafe lock order
  irqchip/sifive-plic: Fix maximum priority threshold value
  irqchip/ti-sci-inta: Fix processing of masked irqs
  irqchip/mbigen: Free msi_desc on device teardown
  irqchip/gic-v4.1: Update effective affinity of virtual SGIs
  irqchip/gic-v4.1: Add support for VPENDBASER's Dirty+Valid signaling
  genirq: Remove setup_irq() and remove_irq()

Pull scheduler fixes from Thomas Gleixner:
 "Two fixes for the scheduler:

   - Work around an uninitialized variable warning where GCC can't
     figure it out.

   - Allow 'isolcpus=' to skip unknown subparameters so that older
     kernels work with the commandline of a newer kernel. Improve the
     error output while at it"

* tag 'sched-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/vtime: Work around an unitialized variable warning
  sched/isolation: Allow "isolcpus=" to skip unknown sub-parameters

Pull RCU fix from Thomas Gleixner:
 "A single bugfix for RCU to prevent taking a lock in NMI context"

* tag 'core-urgent-2020-04-19' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  rcu: Don't acquire lock in NMI handler in rcu_nmi_enter_common()

Pull ext4 fixes from Ted Ts'o:
 "Miscellaneous bug fixes and cleanups for ext4, including a fix for
  generic/388 in data=journal mode, removing some BUG_ON's, and cleaning
  up some compiler warnings"

* tag 'ext4_for_linus_stable' of git://git.kernel.org/pub/scm/linux/kernel/git/tytso/ext4:
  ext4: convert BUG_ON's to WARN_ON's in mballoc.c
  ext4: increase wait time needed before reuse of deleted inode numbers
  ext4: remove set but not used variable 'es' in ext4_jbd2.c
  ext4: remove set but not used variable 'es'
  ext4: do not zeroout extents beyond i_disksize
  ext4: fix return-value types in several function comments
  ext4: use non-movable memory for superblock readahead
  ext4: use matching invalidatepage in ext4_writepage

Pull cifs fixes from Steve French:
 "Three small smb3 fixes: two debug related (helping network tracing for
  SMB2 mounts, and the other removing an unintended debug line on
  signing failures), and one fixing a performance problem with 64K
  pages"

* tag '5.7-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6:
  smb3: remove overly noisy debug line in signing errors
  cifs: improve read performance for page size 64KB & cache=strict & vers=2.1+
  cifs: dump the session id and keys also for SMB2 sessions

Merge tag 'flexible-array-member-5.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux

Pull flexible-array member conversion from Gustavo Silva:
 "The current codebase makes use of the zero-length array language
  extension to the C90 standard, but the preferred mechanism to declare
  variable-length types such as these ones is a flexible array
  member[1][2], introduced in C99:

    struct foo {
        int stuff;
        struct boo array[];
    };

  By making use of the mechanism above, we will get a compiler warning
  in case the flexible array does not occur last in the structure, which
  will help us prevent some kind of undefined behavior bugs from being
  inadvertently introduced[3] to the codebase from now on.

  Also, notice that, dynamic memory allocations won't be affected by
  this change:

   "Flexible array members have incomplete type, and so the sizeof
    operator may not be applied. As a quirk of the original
    implementation of zero-length arrays, sizeof evaluates to zero."[1]

  sizeof(flexible-array-member) triggers a warning because flexible
  array members have incomplete type[1]. There are some instances of
  code in which the sizeof operator is being incorrectly/erroneously
  applied to zero-length arrays and the result is zero. Such instances
  may be hiding some bugs. So, this work (flexible-array member
  convertions) will also help to get completely rid of those sorts of
  issues.

  Notice that all of these patches have been baking in linux-next for
  quite a while now and, 238 more of these patches have already been
  merged into 5.7-rc1.

  There are a couple hundred more of these issues waiting to be
  addressed in the whole codebase"

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")

* tag 'flexible-array-member-5.7-rc2' of git://git.kernel.org/pub/scm/linux/kernel/git/gustavoars/linux: (28 commits)
  xattr.h: Replace zero-length array with flexible-array member
  uapi: linux: fiemap.h: Replace zero-length array with flexible-array member
  uapi: linux: dlm_device.h: Replace zero-length array with flexible-array member
  tpm_eventlog.h: Replace zero-length array with flexible-array member
  ti_wilink_st.h: Replace zero-length array with flexible-array member
  swap.h: Replace zero-length array with flexible-array member
  skbuff.h: Replace zero-length array with flexible-array member
  sched: topology.h: Replace zero-length array with flexible-array member
  rslib.h: Replace zero-length array with flexible-array member
  rio.h: Replace zero-length array with flexible-array member
  posix_acl.h: Replace zero-length array with flexible-array member
  platform_data: wilco-ec.h: Replace zero-length array with flexible-array member
  memcontrol.h: Replace zero-length array with flexible-array member
  list_lru.h: Replace zero-length array with flexible-array member
  lib: cpu_rmap: Replace zero-length array with flexible-array member
  irq.h: Replace zero-length array with flexible-array member
  ihex.h: Replace zero-length array with flexible-array member
  igmp.h: Replace zero-length array with flexible-array member
  genalloc.h: Replace zero-length array with flexible-array member
  ethtool.h: Replace zero-length array with flexible-array member
  ...

Pull SCSI fixes from James Bottomley:
 "Seven fixes: three in target, one on a sg error leg, two in qla2xxx
  fixing warnings introduced in the last merge window and updating
  MAINTAINERS and one in hisi_sas fixing a problem introduced by libata"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  scsi: sg: add sg_remove_request in sg_common_write
  scsi: target: tcmu: reset_ring should reset TCMU_DEV_BIT_BROKEN
  scsi: target: fix PR IN / READ FULL STATUS for FC
  scsi: target: Write NULL to *port_nexus_ptr if no ISID
  scsi: MAINTAINERS: Update qla2xxx FC-SCSI driver maintainer
  scsi: qla2xxx: Fix regression warnings
  scsi: hisi_sas: Fix build error without SATA_HOST

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>