forge/linux-uconsole
1
0
Fork 0
Code Issues 1 Pull requests Projects Releases Packages Wiki Activity Actions
Linux kernel for uConsole
787,965 commits 5 branches 3 tags 4.3 GiB
Find a file
Al Viro e9e47779aa Fix aio_poll() races 
commit af5c72b1fc upstream.

aio_poll() has to cope with several unpleasant problems:
	* requests that might stay around indefinitely need to
be made visible for io_cancel(2); that must not be done to
a request already completed, though.
	* in cases when ->poll() has placed us on a waitqueue,
wakeup might have happened (and request completed) before ->poll()
returns.
	* worse, in some early wakeup cases request might end
up re-added into the queue later - we can't treat "woken up and
currently not in the queue" as "it's not going to stick around
indefinitely"
	* ... moreover, ->poll() might have decided not to
put it on any queues to start with, and that needs to be distinguished
from the previous case
	* ->poll() might have tried to put us on more than one queue.
Only the first will succeed for aio poll, so we might end up missing
wakeups.  OTOH, we might very well notice that only after the
wakeup hits and request gets completed (all before ->poll() gets
around to the second poll_wait()).  In that case it's too late to
decide that we have an error.

req->woken was an attempt to deal with that.  Unfortunately, it was
broken.  What we need to keep track of is not that wakeup has happened -
the thing might come back after that.  It's that async reference is
already gone and won't come back, so we can't (and needn't) put the
request on the list of cancellables.

The easiest case is "request hadn't been put on any waitqueues"; we
can tell by seeing NULL apt.head, and in that case there won't be
anything async.  We should either complete the request ourselves
(if vfs_poll() reports anything of interest) or return an error.

In all other cases we get exclusion with wakeups by grabbing the
queue lock.

If request is currently on queue and we have something interesting
from vfs_poll(), we can steal it and complete the request ourselves.

If it's on queue and vfs_poll() has not reported anything interesting,
we either put it on the cancellable list, or, if we know that it
hadn't been put on all queues ->poll() wanted it on, we steal it and
return an error.

If it's _not_ on queue, it's either been already dealt with (in which
case we do nothing), or there's aio_poll_complete_work() about to be
executed.  In that case we either put it on the cancellable list,
or, if we know it hadn't been put on all queues ->poll() wanted it on,
simulate what cancel would've done.

It's a lot more convoluted than I'd like it to be.  Single-consumer APIs
suck, and unfortunately aio is not an exception...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-05-02 09:58:59 +02:00
arch powerpc/mm/radix: Make Radix require HUGETLB_PAGE 2019-05-02 09:58:55 +02:00
block blk-iolatency: #include "blk.h" 2019-04-20 09:15:58 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: x86/poly1305 - fix overflow during partial reduction 2019-04-27 09:36:37 +02:00
Documentation ARM: 8833/1: Ensure that NEON code always compiles with Clang 2019-04-05 22:33:08 +02:00
drivers fm10k: Fix a potential NULL pointer dereference 2019-05-02 09:58:57 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs Fix aio_poll() races 2019-05-02 09:58:59 +02:00
include aio: simplify - and fix - fget/fput for io_submit() 2019-05-02 09:58:58 +02:00
init Revert "mm: use early_pfn_to_nid in page_ext_init" 2019-03-23 20:09:46 +01:00
ipc ipc/shm.c: use ERR_CAST() for shm_lock() error return 2018-10-05 16:32:04 -07:00
kernel sched/deadline: Correctly handle active 0-lag timers 2019-05-02 09:58:56 +02:00
lib lib/Kconfig.debug: fix build error without CONFIG_BLOCK 2019-05-02 09:58:53 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm percpu: stop printing kernel addresses 2019-04-27 09:36:40 +02:00
net rxrpc: fix race condition in rxrpc_input_packet() 2019-05-02 09:58:57 +02:00
samples samples: mei: use /dev/mei0 instead of /dev/mei 2019-02-15 08:10:11 +01:00
scripts modpost: file2alias: check prototype of handler 2019-04-27 09:36:39 +02:00
security device_cgroup: fix RCU imbalance in error case 2019-04-27 09:36:40 +02:00
sound ALSA: hda/ca0132 - Fix build error without CONFIG_PCI 2019-05-02 09:58:52 +02:00
tools tools include: Adopt linux/bits.h 2019-04-27 09:36:40 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: Reject device ioctls from processes other than the VM's creator 2019-04-03 06:26:29 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile Linux 4.19.37 2019-04-27 09:36:41 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

README 

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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.