Prior to big pcluster, there was only one compressed page so it'd
easy to map this. However, when big pcluster is enabled, more work
needs to be done to handle multiple compressed pages. In detail,

 - (maptype 0) if there is only one compressed page + no need
   to copy inplace I/O, just map it directly what we did before;

 - (maptype 1) if there are more compressed pages + no need to
   copy inplace I/O, vmap such compressed pages instead;

 - (maptype 2) if inplace I/O needs to be copied, use per-CPU
   buffers for decompression then.

Another thing is how to detect inplace decompression is feasable or
not (it's still quite easy for non big pclusters), apart from the
inplace margin calculation, inplace I/O page reusing order is also
needed to be considered for each compressed page. Currently, if the
compressed page is the xth page, it shouldn't be reused as [0 ...
nrpages_out - nrpages_in + x], otherwise a full copy will be triggered.

Although there are some extra optimization ideas for this, I'd like
to make big pcluster work correctly first and obviously it can be
further optimized later since it has nothing with the on-disk format
at all.

Link: https://lore.kernel.org/r/20210407043927.10623-10-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Different from non-compact indexes, several lclusters are packed
as the compact form at once and an unique base blkaddr is stored for
each pack, so each lcluster index would take less space on avarage
(e.g. 2 bytes for COMPACT_2B.) btw, that is also why BIG_PCLUSTER
switch should be consistent for compact head0/1.

Prior to big pcluster, the size of all pclusters was 1 lcluster.
Therefore, when a new HEAD lcluster was scanned, blkaddr would be
bumped by 1 lcluster. However, that way doesn't work anymore for
big pcluster since we actually don't know the compressed size of
pclusters in advance (before reading CBLKCNT lcluster).

So, instead, let blkaddr of each pack be the first pcluster blkaddr
with a valid CBLKCNT, in detail,

 1) if CBLKCNT starts at the pack, this first valid pcluster is
    itself, e.g.
  _____________________________________________________________
 |_CBLKCNT0_|_NONHEAD_| .. |_HEAD_|_CBLKCNT1_| ... |_HEAD_| ...
 ^ = blkaddr base          ^ += CBLKCNT0           ^ += CBLKCNT1

 2) if CBLKCNT doesn't start at the pack, the first valid pcluster
    is the next pcluster, e.g.
  _________________________________________________________
 | NONHEAD_| .. |_HEAD_|_CBLKCNT0_| ... |_HEAD_|_HEAD_| ...
                ^ = blkaddr base        ^ += CBLKCNT0
                                               ^ += 1

When a CBLKCNT is found, blkaddr will be increased by CBLKCNT
lclusters, or a new HEAD is found immediately, bump blkaddr by 1
instead (see the picture above.)

Also noted if CBLKCNT is the end of the pack, instead of storing
delta1 (distance of the next HEAD lcluster) as normal NONHEADs,
it still uses the compressed block count (delta0) since delta1
can be calculated indirectly but the block count can't.

Adjust decoding logic to fit big pcluster compact indexes as well.

Link: https://lore.kernel.org/r/20210407043927.10623-9-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

When INCOMPAT_BIG_PCLUSTER sb feature is enabled, legacy compress indexes
will also have the same on-disk header compact indexes to keep per-file
configurations instead of leaving it zeroed.

If ADVISE_BIG_PCLUSTER is set for a file, CBLKCNT will be loaded for each
pcluster in this file by parsing 1st non-head lcluster.

Link: https://lore.kernel.org/r/20210407043927.10623-8-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Adjust per-CPU buffers on demand since big pcluster definition is
available. Also, bail out unsupported pcluster size according to
Z_EROFS_PCLUSTER_MAX_SIZE.

Link: https://lore.kernel.org/r/20210407043927.10623-7-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Big pcluster indicates the size of compressed data for each physical
pcluster is no longer fixed as block size, but could be more than 1
block (more accurately, 1 logical pcluster)

When big pcluster feature is enabled for head0/1, delta0 of the 1st
non-head lcluster index will keep block count of this pcluster in
lcluster size instead of 1. Or, the compressed size of pcluster
should be 1 lcluster if pcluster has no non-head lcluster index.

Also note that BIG_PCLUSTER feature reuses COMPR_CFGS feature since
it depends on COMPR_CFGS and will be released together.

Link: https://lore.kernel.org/r/20210407043927.10623-6-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

When picking up inplace I/O pages, it should be traversed in reverse
order in aligned with the traversal order of file-backed online pages.
Also, index should be updated together when preloading compressed pages.

Previously, only page-sized pclustersize was supported so no problem
at all. Also rename `compressedpages' to `icpage_ptr' to reflect its
functionality.

Link: https://lore.kernel.org/r/20210407043927.10623-5-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Since multiple pcluster sizes could be used at once, the number of
compressed pages will become a variable factor. It's necessary to
introduce slab pools rather than a single slab cache now.

This limits the pclustersize to 1M (Z_EROFS_PCLUSTER_MAX_SIZE), and
get rid of the obsolete EROFS_FS_CLUSTER_PAGE_LIMIT, which has no
use now.

Link: https://lore.kernel.org/r/20210407043927.10623-4-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

To deal the with the cases which inplace decompression is infeasible
for some inplace I/O. Per-CPU buffers was introduced to get rid of page
allocation latency and thrash for low-latency decompression algorithms
such as lz4.

For the big pcluster feature, introduce multipage per-CPU buffers to
keep such inplace I/O pclusters temporarily as well but note that
per-CPU pages are just consecutive virtually.

When a new big pcluster fs is mounted, its max pclustersize will be
read and per-CPU buffers can be growed if needed. Shrinking adjustable
per-CPU buffers is more complex (because we don't know if such size
is still be used), so currently just release them all when unloading.

Link: https://lore.kernel.org/r/20210409190630.19569-1-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Formal big pcluster design is actually more powerful / flexable than
the previous thought whose pclustersize was fixed as power-of-2 blocks,
which was obviously inefficient and space-wasting. Instead, pclustersize
can now be set independently for each pcluster, so various pcluster
sizes can also be used together in one file if mkfs wants (for example,
according to data type and/or compression ratio).

Let's get rid of previous physical_clusterbits[] setting (also notice
that corresponding on-disk fields are still 0 for now). Therefore,
head1/2 can be used for at most 2 different algorithms in one file and
again pclustersize is now independent of these.

Link: https://lore.kernel.org/r/20210407043927.10623-2-xiang@kernel.orgAcked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

zmap.c: s/correspoinding/corresponding
zdata.c: s/endding/ending

Link: https://lore.kernel.org/r/20210331093920.31923-1-gongruiqi1@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Ruiqi Gong <gongruiqi1@huawei.com>
Reviewed-by: Gao Xiang <hsiangkao@redhat.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Add a bitmap for available compression algorithms and a variable-sized
on-disk table for compression options in preparation for upcoming big
pcluster and LZMA algorithm, which follows the end of super block.

To parse the compression options, the bitmap is scanned one by one.
For each available algorithm, there is data followed by 2-byte `length'
correspondingly (it's enough for most cases, or entire fs blocks should
be used.)

With such available algorithm bitmap, kernel itself can also refuse to
mount such filesystem if any unsupported compression algorithm exists.

Note that COMPR_CFGS feature will be enabled with BIG_PCLUSTER.

Link: https://lore.kernel.org/r/20210329100012.12980-1-hsiangkao@aol.comReviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Introduce z_erofs_lz4_cfgs to store all lz4 configurations.
Currently it's only max_distance, but will be used for new
features later.

Link: https://lore.kernel.org/r/20210329012308.28743-4-hsiangkao@aol.comReviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

lz4 uses LZ4_DISTANCE_MAX to record history preservation. When
using rolling decompression, a block with a higher compression
ratio will cause a larger memory allocation (up to 64k). It may
cause a large resource burden in extreme cases on devices with
small memory and a large number of concurrent IOs. So appropriately
reducing this value can improve performance.

Decreasing this value will reduce the compression ratio (except
when input_size <LZ4_DISTANCE_MAX). But considering that erofs
currently only supports 4k output, reducing this value will not
significantly reduce the compression benefits.

The maximum value of LZ4_DISTANCE_MAX defined by lz4 is 64k, and
we can only reduce this value. For the old kernel, it just can't
reduce the memory allocation during rolling decompression without
affecting the decompression result.

Link: https://lore.kernel.org/r/20210329012308.28743-3-hsiangkao@aol.comReviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
[ Gao Xiang: introduce struct erofs_sb_lz4_info for configurations. ]
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Introduce erofs_sb_has_xxx() to make long checks short, especially
for later big pcluster & LZMA features.

Link: https://lore.kernel.org/r/20210329012308.28743-2-hsiangkao@aol.comReviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

If any unknown i_format fields are set (may be of some new incompat
inode features), mark such inode as unsupported.

Just in case of any new incompat i_format fields added in the future.

Link: https://lore.kernel.org/r/20210329003614.6583-1-hsiangkao@aol.com
Fixes: 431339ba ("staging: erofs: add inode operations")
Cc: <stable@vger.kernel.org> # 4.19+
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Currently, erofs_map_blocks() will be called only from
erofs_{bmap, read_raw_page} which are all for uncompressed files.
So, the compression branch in erofs_map_blocks() is pointless. Let's
remove it and use erofs_map_blocks_flatmode() directly. Also update
related comments.

Link: https://lore.kernel.org/r/20210325071008.573-1-zbestahu@gmail.comReviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Yue Hu <huyue2@yulong.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Add a missing case which could cause unnecessary page allocation but
not directly use inplace I/O instead, which increases runtime extra
memory footprint.

The detail is, considering an online file-backed page, the right half
of the page is chosen to be cached (e.g. the end page of a readahead
request) and some of its data doesn't exist in managed cache, so the
pcluster will be definitely kept in the submission chain. (IOWs, it
cannot be decompressed without I/O, e.g., due to the bypass queue).

Currently, DELAYEDALLOC/TRYALLOC cases can be downgraded as NOINPLACE,
and stop online pages from inplace I/O. After this patch, unneeded page
allocations won't be observed in pickup_page_for_submission() then.

Link: https://lore.kernel.org/r/20210321183227.5182-1-hsiangkao@aol.comSigned-off-by: Gao Xiang <hsiangkao@redhat.com>

Sync decompression was introduced to get rid of additional kworker
scheduling overhead. But there is no such overhead in non-atomic
contexts. Therefore, it should be better to turn off sync decompression
to avoid the current thread waiting in z_erofs_runqueue.

Link: https://lore.kernel.org/r/20210317035448.13921-3-huangjianan@oppo.comReviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

z_erofs_decompressqueue_endio may not be executed in the atomic
context, for example, when dm-verity is turned on. In this scenario,
data can be decompressed directly to get rid of additional kworker
scheduling overhead.

Link: https://lore.kernel.org/r/20210317035448.13921-2-huangjianan@oppo.comReviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Currently, err would be treated as io error. Therefore, it'd be
better to ensure memory allocation during rolling decompression
to avoid such io error.

In the long term, we might consider adding another !Uptodate case
for such case.

Link: https://lore.kernel.org/r/20210316031515.90954-1-huangjianan@oppo.comReviewed-by: Gao Xiang <hsiangkao@redhat.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@redhat.com>

Merge tag 'perf-tools-fixes-for-v5.12-2020-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux

Pull perf tooling fixes from Arnaldo Carvalho de Melo:

 - Avoid write of uninitialized memory when generating PERF_RECORD_MMAP*
   records.

 - Fix 'perf top' BPF support related crash with perf_event_paranoid=3 +
   kptr_restrict.

 - Validate raw event with sysfs exported format bits.

 - Fix waipid on SIGCHLD delivery bugs in 'perf daemon'.

 - Change to use bash for daemon test on Debian, where the default is
   dash and thus fails for use of bashisms in this test.

 - Fix memory leak in vDSO found using ASAN.

 - Remove now useless (due to the fact that BPF now supports static
   vars) failing sub test "BPF relocation checker".

 - Fix auxtrace queue conflict.

 - Sync linux/kvm.h with the kernel sources.

* tag 'perf-tools-fixes-for-v5.12-2020-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux:
  perf test: Change to use bash for daemon test
  perf record: Fix memory leak in vDSO found using ASAN
  perf test: Remove now useless failing sub test "BPF relocation checker"
  perf daemon: Return from kill functions
  perf daemon: Force waipid for all session on SIGCHLD delivery
  perf top: Fix BPF support related crash with perf_event_paranoid=3 + kptr_restrict
  perf pmu: Validate raw event with sysfs exported format bits
  perf synthetic events: Avoid write of uninitialized memory when generating PERF_RECORD_MMAP* records
  tools headers UAPI: Sync linux/kvm.h with the kernel sources
  perf synthetic-events: Fix uninitialized 'kernel_thread' variable
  perf auxtrace: Fix auxtrace queue conflict

Pull auxdisplay fix from Miguel Ojeda:
 "Remove in_interrupt() usage (Sebastian Andrzej Siewior)"

* tag 'auxdisplay-for-linus-v5.12-rc6' of git://github.com/ojeda/linux:
  auxdisplay: Remove in_interrupt() usage.

Pull x86 fixes from Ingo Molnar:
 "Two fixes:

   - Fix build failure on Ubuntu with new GCC packages that turn
     on -fcf-protection

   - Fix SME memory encryption PTE encoding bug - AFAICT the code
     worked on 4K page sizes (level 1) but had the wrong shift at
     higher page level orders (level 2 and higher)"

* tag 'x86-urgent-2021-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/build: Turn off -fcf-protection for realmode targets
  x86/mem_encrypt: Correct physical address calculation in __set_clr_pte_enc()

Pull locking fix from Ingo Molnar:
 "Fix the non-debug mutex_lock_io_nested() method to map to
  mutex_lock_io() instead of mutex_lock().

  Right now nothing uses this API explicitly, but this is an
  accident waiting to happen"

* tag 'locking-urgent-2021-03-28' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  locking/mutex: Fix non debug version of mutex_lock_io_nested()

Pull cifs fixes from Steve French:
 "Five cifs/smb3 fixes, two for stable.

  Includes an important fix for encryption and an ACL fix, as well as a
  fix for possible reflink data corruption"

* tag '5.12-rc4-smb3' of git://git.samba.org/sfrench/cifs-2.6:
  smb3: fix cached file size problems in duplicate extents (reflink)
  cifs: Silently ignore unknown oplock break handle
  cifs: revalidate mapping when we open files for SMB1 POSIX
  cifs: Fix chmod with modefromsid when an older ACE already exists.
  cifs: Adjust key sizes and key generation routines for AES256 encryption

Pull io_uring fixes from Jens Axboe:

 - Use thread info versions of flag testing, as discussed last week.

 - The series enabling PF_IO_WORKER to just take signals, instead of
   needing to special case that they do not in a bunch of places. Ends
   up being pretty trivial to do, and then we can revert all the special
   casing we're currently doing.

 - Kill dead pointer assignment

 - Fix hashed part of async work queue trace

 - Fix sign extension issue for IORING_OP_PROVIDE_BUFFERS

 - Fix a link completion ordering regression in this merge window

 - Cancellation fixes

* tag 'io_uring-5.12-2021-03-27' of git://git.kernel.dk/linux-block:
  io_uring: remove unsued assignment to pointer io
  io_uring: don't cancel extra on files match
  io_uring: don't cancel-track common timeouts
  io_uring: do post-completion chore on t-out cancel
  io_uring: fix timeout cancel return code
  Revert "signal: don't allow STOP on PF_IO_WORKER threads"
  Revert "kernel: freezer should treat PF_IO_WORKER like PF_KTHREAD for freezing"
  Revert "kernel: treat PF_IO_WORKER like PF_KTHREAD for ptrace/signals"
  Revert "signal: don't allow sending any signals to PF_IO_WORKER threads"
  kernel: stop masking signals in create_io_thread()
  io_uring: handle signals for IO threads like a normal thread
  kernel: don't call do_exit() for PF_IO_WORKER threads
  io_uring: maintain CQE order of a failed link
  io-wq: fix race around pending work on teardown
  io_uring: do ctx sqd ejection in a clear context
  io_uring: fix provide_buffers sign extension
  io_uring: don't skip file_end_write() on reissue
  io_uring: correct io_queue_async_work() traces
  io_uring: don't use {test,clear}_tsk_thread_flag() for current

Pull block fixes from Jens Axboe:

 - Fix regression from this merge window with the xarray partition
   change, which allowed partition counts that overflow the u8 that
   holds the partition number (Ming)

 - Fix zone append warning (Johannes)

 - Segmentation count fix for multipage bvecs (David)

 - Partition scan fix (Chris)

* tag 'block-5.12-2021-03-27' of git://git.kernel.dk/linux-block:
  block: don't create too many partitions
  block: support zone append bvecs
  block: recalculate segment count for multi-segment discards correctly
  block: clear GD_NEED_PART_SCAN later in bdev_disk_changed

Pull SCSI fixes from James Bottomley:
 "Seven fixes, all in drivers (qla2xxx, mkt3sas, qedi, target,
  ibmvscsi).

  The most serious are the target pscsi oom and the qla2xxx revert which
  can otherwise cause a use after free"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  scsi: target: pscsi: Clean up after failure in pscsi_map_sg()
  scsi: target: pscsi: Avoid OOM in pscsi_map_sg()
  scsi: mpt3sas: Fix error return code of mpt3sas_base_attach()
  scsi: qedi: Fix error return code of qedi_alloc_global_queues()
  scsi: Revert "qla2xxx: Make sure that aborted commands are freed"
  scsi: ibmvfc: Make ibmvfc_wait_for_ops() MQ aware
  scsi: ibmvfc: Fix potential race in ibmvfc_wait_for_ops()

There is an assignment to io that is never read after the assignment,
the assignment is redundant and can be removed.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

As tasks always wait and kill their io-wq on exec/exit, files are of no
more concern to us, so we don't need to specifically cancel them by hand
in those cases. Moreover we should not, because io_match_task() looks at
req->task->files now, which is always true and so leads to extra
cancellations, that wasn't a case before per-task io-wq.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/0566c1de9b9dd417f5de345c817ca953580e0e2e.1616696997.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Don't account usual timeouts (i.e. not linked) as REQ_F_INFLIGHT but
keep behaviour prior to dd59a3d5 ("io_uring: reliably cancel linked
timeouts").
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/104441ef5d97e3932113d44501fda0df88656b83.1616696997.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

Don't forget about io_commit_cqring() + io_cqring_ev_posted() after
exit/exec cancelling timeouts. Both functions declared only after
io_kill_timeouts(), so to avoid tons of forward declarations move
it down.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/72ace588772c0f14834a6a4185d56c445a366fb4.1616696997.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

When we cancel a timeout we should emit a sensible return code, like
-ECANCELED but not 0, otherwise it may trick users.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/7b0ad1065e3bd1994722702bd0ba9e7bc9b0683b.1616696997.git.asml.silence@gmail.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

This reverts commit 4db4b1a0.

The IO threads allow and handle SIGSTOP now, so don't special case them
anymore in task_set_jobctl_pending().
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This reverts commit 15b2219f.

Before IO threads accepted signals, the freezer using take signals to wake
up an IO thread would cause them to loop without any way to clear the
pending signal. That is no longer the case, so stop special casing
PF_IO_WORKER in the freezer.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This reverts commit 6fb8f43c.

The IO threads do allow signals now, including SIGSTOP, and we can allow
ptrace attach. Attaching won't reveal anything interesting for the IO
threads, but it will allow eg gdb to attach to a task with io_urings
and IO threads without complaining. And once attached, it will allow
the usual introspection into regular threads.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This reverts commit 5be28c8f.

IO threads now take signals just fine, so there's no reason to limit them
specifically. Revert the change that prevented that from happening.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

This is racy - move the blocking into when the task is created and
we're marking it as PF_IO_WORKER anyway. The IO threads are now
prepared to handle signals like SIGSTOP as well, so clear that from
the mask to allow proper stopping of IO threads.
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Reported-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

We go through various hoops to disallow signals for the IO threads, but
there's really no reason why we cannot just allow them. The IO threads
never return to userspace like a normal thread, and hence don't go through
normal signal processing. Instead, just check for a pending signal as part
of the work loop, and call get_signal() to handle it for us if anything
is pending.

With that, we can support receiving signals, including special ones like
SIGSTOP.
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>