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Roman Penyaev 65759097d8 epoll: call final ep_events_available() check under the lock 
There is a possible race when ep_scan_ready_list() leaves ->rdllist and
->obflist empty for a short period of time although some events are
pending.  It is quite likely that ep_events_available() observes empty
lists and goes to sleep.

Since commit 339ddb53d3 ("fs/epoll: remove unnecessary wakeups of
nested epoll") we are conservative in wakeups (there is only one place
for wakeup and this is ep_poll_callback()), thus ep_events_available()
must always observe correct state of two lists.

The easiest and correct way is to do the final check under the lock.
This does not impact the performance, since lock is taken anyway for
adding a wait entry to the wait queue.

The discussion of the problem can be found here:

   https://lore.kernel.org/linux-fsdevel/a2f22c3c-c25a-4bda-8339-a7bdaf17849e@akamai.com/

In this patch barrierless __set_current_state() is used.  This is safe
since waitqueue_active() is called under the same lock on wakeup side.

Short-circuit for fatal signals (i.e.  fatal_signal_pending() check) is
moved to the line just before actual events harvesting routine.  This is
fully compliant to what is said in the comment of the patch where the
actual fatal_signal_pending() check was added: c257a340ed ("fs, epoll:
short circuit fetching events if thread has been killed").

Fixes: 339ddb53d3 ("fs/epoll: remove unnecessary wakeups of nested epoll")
Reported-by: Jason Baron <jbaron@akamai.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Roman Penyaev <rpenyaev@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jason Baron <jbaron@akamai.com>
Cc: Khazhismel Kumykov <khazhy@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200505145609.1865152-1-rpenyaev@suse.de
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2020-05-14 10:00:35 -07:00
arch A set of fixes for x86: 2020-05-10 11:59:53 -07:00
block bdi: use bdi_dev_name() to get device name 2020-05-09 16:07:39 -06:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto gcc-10: avoid shadowing standard library 'free()' in crypto 2020-05-09 15:58:04 -07:00
Documentation Bugfixes, mostly for ARM and AMD, and more documentation. 2020-05-07 09:50:59 -07:00
drivers Some GPIO fixes for the v5.7 kernel: 2020-05-12 10:39:34 -07:00
fs epoll: call final ep_events_available() check under the lock 2020-05-14 10:00:35 -07:00
include mm, memcg: fix inconsistent oom event behavior 2020-05-14 10:00:35 -07:00
init Tracing fixes to previous fixes: 2020-05-12 11:06:26 -07:00
ipc ipc/mqueue.c: change __do_notify() to bypass check_kill_permission() 2020-05-07 19:27:20 -07:00
kernel Tracing fixes to previous fixes: 2020-05-12 11:06:26 -07:00
lib ubsan: disable UBSAN_ALIGNMENT under COMPILE_TEST 2020-05-07 19:27:21 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm block-5.7-2020-05-09 2020-05-10 11:16:07 -07:00
net Fixes: 2020-05-11 12:04:52 -07:00
samples tracing: Fix doc mistakes in trace sample 2020-05-07 13:32:57 -04:00
scripts scripts/gdb: repair rb_first() and rb_last() 2020-05-07 19:27:20 -07:00
security selinux/stable-5.7 PR 20200430 2020-04-30 16:35:45 -07:00
sound sound fixes for 5.7-rc4 2020-05-01 11:05:28 -07:00
tools Tracing fixes to previous fixes: 2020-05-12 11:06:26 -07:00
usr kbuild: fix comment about missing include guard detection 2020-04-11 12:09:48 +09:00
virt KVM: arm64: Fix 32bit PC wrap-around 2020-05-01 09:51:08 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2020-04-18 13:49:33 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
.mailmap mailmap: Add Sedat Dilek (replacement for expired email address) 2020-04-11 09:28:34 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Hand MIPS over to Thomas 2020-02-24 22:43:18 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Fixes for an endianness handling bug that prevented mounts on 2020-05-08 10:27:00 -07:00
Makefile Linux 5.7-rc5 2020-05-10 15:16:58 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -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.

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.