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  1. Apr 16, 2022
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    • Igor Pylypiv's avatar
      Revert "module, async: async_synchronize_full() on module init iff async is used" · dc8da50c
      Igor Pylypiv authored 
      
stable inclusion
from linux-4.19.231
commit a0c66ac8b72f816d5631fde0ca0b39af602dce48

--------------------------------

[ Upstream commit 67d6212afda218d564890d1674bab28e8612170f ]

This reverts commit 774a1221.

We need to finish all async code before the module init sequence is
done.  In the reverted commit the PF_USED_ASYNC flag was added to mark a
thread that called async_schedule().  Then the PF_USED_ASYNC flag was
used to determine whether or not async_synchronize_full() needs to be
invoked.  This works when modprobe thread is calling async_schedule(),
but it does not work if module dispatches init code to a worker thread
which then calls async_schedule().

For example, PCI driver probing is invoked from a worker thread based on
a node where device is attached:

	if (cpu < nr_cpu_ids)
		error = work_on_cpu(cpu, local_pci_probe, &ddi);
	else
		error = local_pci_probe(&ddi);

We end up in a situation where a worker thread gets the PF_USED_ASYNC
flag set instead of the modprobe thread.  As a result,
async_synchronize_full() is not invoked and modprobe completes without
waiting for the async code to finish.

The issue was discovered while loading the pm80xx driver:
(scsi_mod.scan=async)

modprobe pm80xx                      worker
...
  do_init_module()
  ...
    pci_call_probe()
      work_on_cpu(local_pci_probe)
                                     local_pci_probe()
                                       pm8001_pci_probe()
                                         scsi_scan_host()
                                           async_schedule()
                                           worker->flags |= PF_USED_ASYNC;
                                     ...
      < return from worker >
  ...
  if (current->flags & PF_USED_ASYNC) <--- false
  	async_synchronize_full();

Commit 21c3c5d2 ("block: don't request module during elevator init")
fixed the deadlock issue which the reverted commit 774a1221
("module, async: async_synchronize_full() on module init iff async is
used") tried to fix.

Since commit 0fdff3ec ("async, kmod: warn on synchronous
request_module() from async workers") synchronous module loading from
async is not allowed.

Given that the original deadlock issue is fixed and it is no longer
allowed to call synchronous request_module() from async we can remove
PF_USED_ASYNC flag to make module init consistently invoke
async_synchronize_full() unless async module probe is requested.

Signed-off-by: default avatarIgor Pylypiv <ipylypiv@google.com>
Reviewed-by: default avatarChangyuan Lyu <changyuanl@google.com>
Reviewed-by: default avatarLuis Chamberlain <mcgrof@kernel.org>
Acked-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
Signed-off-by: default avatarYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: default avatarLaibin Qiu <qiulaibin@huawei.com>
      4.19.90-2204.2.0
      dc8da50c
    • daniel.starke@siemens.com's avatar
      tty: n_gsm: fix encoding of control signal octet bit DV · be439c06
      daniel.starke@siemens.com authored 
      stable inclusion
from linux-4.19.232
commit 28ca082153794cf5c98e7bb93d7f30f8ba46bec4

--------------------------------

commit 737b0ef3be6b319d6c1fd64193d1603311969326 upstream.

n_gsm is based on the 3GPP 07.010 and its newer version is the 3GPP 27.010.
See https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1516


The changes from 07.010 to 27.010 are non-functional. Therefore, I refer to
the newer 27.010 here. Chapter 5.4.6.3.7 describes the encoding of the
control signal octet used by the MSC (modem status command). The same
encoding is also used in convergence layer type 2 as described in chapter
5.5.2. Table 7 and 24 both require the DV (data valid) bit to be set 1 for
outgoing control signal octets sent by the DTE (data terminal equipment),
i.e. for the initiator side.
Currently, the DV bit is only set if CD (carrier detect) is on, regardless
of the side.

This patch fixes this behavior by setting the DV bit on the initiator side
unconditionally.

Fixes: e1eaea46 ("tty: n_gsm line discipline")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDaniel Starke <daniel.starke@siemens.com>
Link: https://lore.kernel.org/r/20220218073123.2121-1-daniel.starke@siemens.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: default avatarLaibin Qiu <qiulaibin@huawei.com>
      be439c06
    • Linus Torvalds's avatar
      fget: clarify and improve __fget_files() implementation · 8e227868
      Linus Torvalds authored 
      stable inclusion
from linux-4.19.232
commit 400c2f361c25bc092d0636cfa32d0549a181e653

--------------------------------

commit e386dfc56f837da66d00a078e5314bc8382fab83 upstream.

Commit 054aa8d439b9 ("fget: check that the fd still exists after getting
a ref to it") fixed a race with getting a reference to a file just as it
was being closed.  It was a fairly minimal patch, and I didn't think
re-checking the file pointer lookup would be a measurable overhead,
since it was all right there and cached.

But I was wrong, as pointed out by the kernel test robot.

The 'poll2' case of the will-it-scale.per_thread_ops benchmark regressed
quite noticeably.  Admittedly it seems to be a very artificial test:
doing "poll()" system calls on regular files in a very tight loop in
multiple threads.

That means that basically all the time is spent just looking up file
descriptors without ever doing anything useful with them (not that doing
'poll()' on a regular file is useful to begin with).  And as a result it
shows the extra "re-check fd" cost as a sore thumb.

Happily, the regression is fixable by just writing the code to loook up
the fd to be better and clearer.  There's still a cost to verify the
file pointer, but now it's basically in the noise even for that
benchmark that does nothing else - and the code is more understandable
and has better comments too.

[ Side note: this patch is also a classic case of one that looks very
  messy with the default greedy Myers diff - it's much more legible with
  either the patience of histogram diff algorithm ]

Link: https://lore.kernel.org/lkml/20211210053743.GA36420@xsang-OptiPlex-9020/
Link: https://lore.kernel.org/lkml/20211213083154.GA20853@linux.intel.com/


Reported-by: default avatarkernel test robot <oliver.sang@intel.com>
Tested-by: default avatarCarel Si <beibei.si@intel.com>
Cc: Jann Horn <jannh@google.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: default avatarYongqiang Liu <liuyongqiang13@huawei.com>
Signed-off-by: default avatarLaibin Qiu <qiulaibin@huawei.com>
      8e227868