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Frederic Barrat ad7b4e8022 cxl: Fix possible deadlock when processing page faults from cxllib
cxllib_handle_fault() is called by an external driver when it needs to
have the host resolve page faults for a buffer. The buffer can cover
several pages and VMAs. The function iterates over all the pages used
by the buffer, based on the page size of the VMA.

To ensure some stability while processing the faults, the thread T1
grabs the mm->mmap_sem semaphore with read access (R1). However, when
processing a page fault for a single page, one of the underlying
functions, copro_handle_mm_fault(), also grabs the same semaphore with
read access (R2). So the thread T1 takes the semaphore twice.

If another thread T2 tries to access the semaphore in write mode W1
(say, because it wants to allocate memory and calls 'brk'), then that
thread T2 will have to wait because there's a reader (R1). If the
thread T1 is processing a new page at that time, it won't get an
automatic grant at R2, because there's now a writer thread
waiting (T2). And we have a deadlock.

The timeline is:
1. thread T1 owns the semaphore with read access R1
2. thread T2 requests write access W1 and waits
3. thread T1 requests read access R2 and waits

The fix is for the thread T1 to release the semaphore R1 once it got
the information it needs from the current VMA. The address space/VMAs
could evolve while T1 iterates over the full buffer, but in the
unlikely case where T1 misses a page, the external driver will raise a
new page fault when retrying the memory access.

Fixes: 3ced8d7300 ("cxl: Export library to support IBM XSL")
Cc: stable@vger.kernel.org # 4.13+
Signed-off-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2018-04-04 22:09:33 +10:00
arch powerpc/hw_breakpoint: Only disable hw breakpoint if cpu supports it 2018-04-04 21:54:02 +10:00
block for-linus-20180302 2018-03-02 09:35:36 -08:00
certs certs/blacklist_nohashes.c: fix const confusion in certs blacklist 2018-02-21 15:35:43 -08:00
crypto X.509: fix NULL dereference when restricting key with unsupported_sig 2018-02-22 14:38:34 +00:00
Documentation Merge branch 'fixes' into next 2018-03-28 22:59:50 +11:00
drivers cxl: Fix possible deadlock when processing page faults from cxllib 2018-04-04 22:09:33 +10:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs for-4.16-rc3-tag 2018-03-04 11:04:27 -08:00
include Merge branch 'topic/paca' into next 2018-03-31 09:09:36 +11:00
init jump_label: Explicitly disable jump labels in __init code 2018-02-21 16:54:05 +01:00
ipc vfs: do bulk POLL* -> EPOLL* replacement 2018-02-11 14:34:03 -08:00
kernel Merge branch 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-03-04 11:34:49 -08:00
lib lib/raid6: Build proper raid6test files on powerpc 2018-03-20 16:47:52 +11:00
LICENSES LICENSES: Add MPL-1.1 license 2018-01-06 10:59:44 -07:00
mm Merge branch 'topic/paca' into next 2018-03-31 09:09:36 +11:00
net libceph, ceph: avoid memory leak when specifying same option several times 2018-02-26 16:19:30 +01:00
samples - do not build samples when cross compiling (Michal Hocko) 2018-02-27 10:39:29 -08:00
scripts Kbuild fixes for v4.16 2018-03-03 10:37:01 -08:00
security integrity/security: fix digsig.c build error with header file 2018-02-22 20:09:08 -08:00
sound ALSA: x86: Fix potential crash at error path 2018-02-28 08:46:00 +01:00
tools selftests/powerpc: Fix copyloops build since Power4 assembler change 2018-04-03 21:50:09 +10:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt KVM: mmu: Fix overlap between public and private memslots 2018-02-24 01:43:36 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore .gitignore: ignore ASN.1 auto generated files 2018-02-14 21:05:38 +01:00
.mailmap mailmap: update Mark Yao's email address 2018-01-04 16:45:09 -08:00
COPYING
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Kbuild fixes for v4.16 2018-03-03 10:37:01 -08:00
Makefile Linux 4.16-rc4 2018-03-04 14:54:11 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

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.