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Nicolai Stange c4a23c852e io_uring: Fix current->fs handling in io_sq_wq_submit_work() 
No upstream commit, this is a fix to a stable 5.4 specific backport.

The intention of backport commit cac68d12c5 ("io_uring: grab ->fs as part
of async offload") as found in the stable 5.4 tree was to make
io_sq_wq_submit_work() to switch the workqueue task's ->fs over to the
submitting task's one during the IO operation.

However, due to a small logic error, this change turned out to not have any
actual effect. From a high level, the relevant code in
io_sq_wq_submit_work() looks like

  old_fs_struct = current->fs;
  do {
          ...
          if (req->fs != current->fs && current->fs != old_fs_struct) {
                  task_lock(current);
                  if (req->fs)
                          current->fs = req->fs;
                  else
                          current->fs = old_fs_struct;
                  task_unlock(current);
          }
          ...
  } while (req);

The if condition is supposed to cover the case that current->fs doesn't
match what's needed for processing the request, but observe how it fails
to ever evaluate to true due to the second clause:
current->fs != old_fs_struct will be false in the first iteration as per
the initialization of old_fs_struct and because this prevents current->fs
from getting replaced, the same follows inductively for all subsequent
iterations.

Fix said if condition such that
- if req->fs is set and doesn't match current->fs, the latter will be
  switched to the former
- or if req->fs is unset, the switch back to the initial old_fs_struct
  will be made, if necessary.

While at it, also correct the condition for the ->fs related cleanup right
before the return of io_sq_wq_submit_work(): currently, old_fs_struct is
restored only if it's non-NULL. It is always non-NULL though and thus, the
if-condition is rendundant. Supposedly, the motivation had been to optimize
and avoid switching current->fs back to the initial old_fs_struct in case
it is found to have the desired value already. Make it so.

Cc: stable@vger.kernel.org # v5.4
Fixes: cac68d12c5 ("io_uring: grab ->fs as part of async offload")
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 		2021-01-30 13:54:10 +01:00
Documentation x86/xen: Add xen_no_vector_callback option to test PCI INTX delivery 2021-01-27 11:47:45 +01:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch sh: dma: fix kconfig dependency for G2_DMA 2021-01-27 11:47:52 +01:00
block bfq: Fix computation of shallow depth 2021-01-19 18:26:15 +01:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto crypto: asym_tpm: correct zero out potential secrets 2021-01-12 20:16:17 +01:00
drivers HID: wacom: Correct NULL dereference on AES pen proximity 2021-01-30 13:54:10 +01:00
fs io_uring: Fix current->fs handling in io_sq_wq_submit_work() 2021-01-30 13:54:10 +01:00
include tcp: fix TCP_USER_TIMEOUT with zero window 2021-01-27 11:47:55 +01:00
init exec: Transform exec_update_mutex into a rw_semaphore 2021-01-09 13:44:55 +01:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel futex: Handle faults correctly for PI futexes 2021-01-30 13:54:10 +01:00
lib lib/raid6: Let $(UNROLL) rules work with macOS userland 2021-01-19 18:26:15 +01:00
mm Revert "mm/slub: fix a memory leak in sysfs_slab_add()" 2021-01-30 13:54:09 +01:00
net tcp: fix TCP_USER_TIMEOUT with zero window 2021-01-27 11:47:55 +01:00
samples samples: bpf: Fix lwt_len_hist reusing previous BPF map 2020-12-30 11:51:12 +01:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-12 20:16:10 +01:00
security dump_common_audit_data(): fix racy accesses to ->d_name 2021-01-19 18:26:16 +01:00
sound ASoC: Intel: haswell: Add missing pm_ops 2021-01-27 11:47:42 +01:00
tools selftests: net: fib_tests: remove duplicate log test 2021-01-27 11:47:48 +01:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt kvm: check tlbs_dirty directly 2021-01-12 20:16:22 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig
…
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS Documentation/llvm: add documentation on building w/ Clang/LLVM 2020-08-26 10:40:46 +02:00
Makefile Linux 5.4.93 2021-01-27 11:47:55 +01:00
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.