0a01326fdd
[ Upstream commit 67d6212afda218d564890d1674bab28e8612170f ]
This reverts commit 774a1221e862b343388347bac9b318767336b20b.
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 21c3c5d28007 ("block: don't request module during elevator init")
fixed the deadlock issue which the reverted commit 774a1221e862
("module, async: async_synchronize_full() on module init iff async is
used") tried to fix.
Since commit 0fdff3ec6d87 ("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: Igor Pylypiv <ipylypiv@google.com>
Reviewed-by: Changyuan Lyu <changyuanl@google.com>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.