[PATCH v7 00/12 (RESEND)] syfs: generic deadlock fix with module removal
by Luis Chamberlain
(this is a resend as I botched an email and it seems that made it
so that this thread did not end up hitting lkml lists )
This is a follow up to my v6 series of fixes for the zram driver [0]
which ended up uncovering a generic deadlock issue with sysfs and module
removal. I've reported this issue and proposed a few patches first since
March 2021 [1]. At the end of this email you will find an itemized list of
changes since that v1 series.
In this v7 I've decided it is best to merge all the effort together into
one patch set because communication was being lost when I split the
patches up. This was not helping in any way to either fix the zram
issues or come to consensus on a generic solution. The patches are also
merged now because they are all related now.
It turns out that the generic sysfs fix I suspected was possible which I
postulated *since my v1 series days*... proves to have been correct all
along, it just required a bit more love. So this v7 formalizes that generic
effort and drops the macros which were only temporary hacks until a generic
solution was agreed upon. It would seem I'm the only one actually working on
a generic solution to this problem, so here's my attempt to fix that.
Running checkpatch exposed that S_IRWXUGO and S_IRWXU|S_IRUGO|S_IXUGO
should be replaced, so I did that in this series in two new patches. This
v7 series also includes a try_module_get() documentation extension with
tribal knowledge and new information I don't think some folks still believe
in. The new test_sysfs selftest however proves this information to be correct,
the same selftest can be used to try to prove that documentation incorrect.
I'm calling for the generic solution to be agreed upon now, or we decide
a path forward with the macros as temporary for now given this issue is
long over due. Greg's biggest issues with the postulated generic fix was that
the fix was too large. Unfortunately I've tried and I can't figure out a way
to make this smaller. If someone can figure another method I'm eager to see it!
Because the deadlock is now fixed generically, the zram deadlock issue
is easily fixed in the last patch by just using ATTRIBUTE_GROUPS().
These patches can be found in my 20210917-sysfs-generic-deadlock-fix
branch [4], this is all based on linux-next tag 20210917.
On v1:
- Open coded the sysfs deadlock race to only be localized by the zram
driver
Changes on v2:
- used bdgrab() as well for another race which was speculated by Minchan
- improved documentation of fixes
Changes on v3:
- used a localized zram macros for the sysfs attributes instead of
open coding on each routine
- replaced bdget() stuff for a generic get_device() and bus_get() on
dev_attr_show() / dev_attr_store() for the issue speculated by
Michan
Changes on v4:
- Cosmetic fixes on the zram fixes as requested by Greg
- Split out the driver core fix as requested by Greg for the
issue speculated by Michan. This fix ended up getting up to its 4th
patch iteration [2] and eventually hit linux-next. We got a 0day
0day suspend stres fail for this patch [3]
Changes on v5:
- I ended up writing a test_sysfs driver and with it I ended up
proving that the issue speculated by Michen was not possible and
so I asked Greg to drop the patch from his queue titled
"sysfs: fix kobject refcount to address races with kobject removal"
- checkpatch fixes for the zram changes
Changes on v6:
- I submitted my test_sysfs driver for inclusion upstream which easily
abstracted the deadlock issue in a driver generically [4]
- I rebased the zram fixes and added also a new patch for zram to use
ATTRIBUTE_GROUPS As per Minchen I sent the patches to be merged
through Andrew Morton.
- Greg ended up NACK'ing the patchset because he was not sure the fix
was correct still
[0] https://lkml.kernel.org/r/20210703001958.620899-1-mcgrof@kernel.org
[1] https://lkml.kernel.org/r/20210306022035.11266-1-mcgrof@kernel.org
[2] https://lkml.kernel.org/r/20210623215007.862787-1-mcgrof@kernel.org
[3] https://lkml.kernel.org/r/20210701022737.GC21279@xsang-OptiPlex-9020
[4] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log...
Luis Chamberlain (12):
LICENSES: Add the copyleft-next-0.3.1 license
testing: use the copyleft-next-0.3.1 SPDX tag
selftests: add tests_sysfs module
kernfs: add initial failure injection support
test_sysfs: add support to use kernfs failure injection
kernel/module: add documentation for try_module_get()
fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on
kernfs_create_link()
fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755
sysfs_create_dir_ns()
sysfs: fix deadlock race with module removal
test_sysfs: enable deadlock tests by default
zram: fix crashes with cpu hotplug multistate
zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal
.../fault-injection/fault-injection.rst | 22 +
LICENSES/dual/copyleft-next-0.3.1 | 237 +++
MAINTAINERS | 9 +-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 4 +-
drivers/block/zram/zram_drv.c | 74 +-
fs/kernfs/Makefile | 1 +
fs/kernfs/dir.c | 41 +-
fs/kernfs/failure-injection.c | 91 ++
fs/kernfs/file.c | 20 +-
fs/kernfs/kernfs-internal.h | 73 +
fs/kernfs/symlink.c | 4 +-
fs/sysfs/dir.c | 5 +-
fs/sysfs/file.c | 10 +-
fs/sysfs/group.c | 1 +
include/linux/kernfs.h | 16 +-
include/linux/module.h | 34 +-
include/linux/sysfs.h | 52 +-
kernel/cgroup/cgroup.c | 2 +-
lib/Kconfig.debug | 25 +
lib/Makefile | 1 +
lib/test_kmod.c | 12 +-
lib/test_sysctl.c | 12 +-
lib/test_sysfs.c | 974 ++++++++++++
tools/testing/selftests/kmod/kmod.sh | 13 +-
tools/testing/selftests/sysctl/sysctl.sh | 12 +-
tools/testing/selftests/sysfs/Makefile | 12 +
tools/testing/selftests/sysfs/config | 5 +
tools/testing/selftests/sysfs/sysfs.sh | 1383 +++++++++++++++++
28 files changed, 3048 insertions(+), 97 deletions(-)
create mode 100644 LICENSES/dual/copyleft-next-0.3.1
create mode 100644 fs/kernfs/failure-injection.c
create mode 100644 lib/test_sysfs.c
create mode 100644 tools/testing/selftests/sysfs/Makefile
create mode 100644 tools/testing/selftests/sysfs/config
create mode 100755 tools/testing/selftests/sysfs/sysfs.sh
--
2.30.2
2 years, 7 months
- 1
- 12
[PATCH v7 00/12] syfs: generic deadlock fix with module removal
by Luis Chamberlain
This is a follow up to my v6 series of fixes for the zram driver [0]
which ended up uncovering a generic deadlock issue with sysfs and module
removal. I've reported this issue and proposed a few patches first since
March 2021 [1]. At the end of this email you will find an itemized list of
changes since that v1 series.
In this v7 I've decided it is best to merge all the effort together into
one patch set because communication was being lost when I split the
patches up. This was not helping in any way to either fix the zram
issues or come to consensus on a generic solution. The patches are also
merged now because they are all related now.
It turns out that the generic sysfs fix I suspected was possible which I
postulated *since my v1 series days*... proves to have been correct all
along, it just required a bit more love. So this v7 formalizes that generic
effort and drops the macros which were only temporary hacks until a generic
solution was agreed upon. It would seem I'm the only one actually working on
a generic solution to this problem, so here's my attempt to fix that.
Running checkpatch exposed that S_IRWXUGO and S_IRWXU|S_IRUGO|S_IXUGO
should be replaced, so I did that in this series in two new patches. This
v7 series also includes a try_module_get() documentation extension with
tribal knowledge and new information I don't think some folks still believe
in. The new test_sysfs selftest however proves this information to be correct,
the same selftest can be used to try to prove that documentation incorrect.
I'm calling for the generic solution to be agreed upon now, or we decide
a path forward with the macros as temporary for now given this issue is
long over due. Greg's biggest issues with the postulated generic fix was that
the fix was too large. Unfortunately I've tried and I can't figure out a way
to make this smaller. If someone can figure another method I'm eager to see it!
Because the deadlock is now fixed generically, the zram deadlock issue
is easily fixed in the last patch by just using ATTRIBUTE_GROUPS().
These patches can be found in my 20210917-sysfs-generic-deadlock-fix
branch [4], this is all based on linux-next tag 20210917.
On v1:
- Open coded the sysfs deadlock race to only be localized by the zram
driver
Changes on v2:
- used bdgrab() as well for another race which was speculated by Minchan
- improved documentation of fixes
Changes on v3:
- used a localized zram macros for the sysfs attributes instead of
open coding on each routine
- replaced bdget() stuff for a generic get_device() and bus_get() on
dev_attr_show() / dev_attr_store() for the issue speculated by
Michan
Changes on v4:
- Cosmetic fixes on the zram fixes as requested by Greg
- Split out the driver core fix as requested by Greg for the
issue speculated by Michan. This fix ended up getting up to its 4th
patch iteration [2] and eventually hit linux-next. We got a 0day
0day suspend stres fail for this patch [3]
Changes on v5:
- I ended up writing a test_sysfs driver and with it I ended up
proving that the issue speculated by Michen was not possible and
so I asked Greg to drop the patch from his queue titled
"sysfs: fix kobject refcount to address races with kobject removal"
- checkpatch fixes for the zram changes
Changes on v6:
- I submitted my test_sysfs driver for inclusion upstream which easily
abstracted the deadlock issue in a driver generically [4]
- I rebased the zram fixes and added also a new patch for zram to use
ATTRIBUTE_GROUPS As per Minchen I sent the patches to be merged
through Andrew Morton.
- Greg ended up NACK'ing the patchset because he was not sure the fix
was correct still
[0] https://lkml.kernel.org/r/20210703001958.620899-1-mcgrof@kernel.org
[1] https://lkml.kernel.org/r/20210306022035.11266-1-mcgrof@kernel.org
[2] https://lkml.kernel.org/r/20210623215007.862787-1-mcgrof@kernel.org
[3] https://lkml.kernel.org/r/20210701022737.GC21279@xsang-OptiPlex-9020
[4] https://git.kernel.org/pub/scm/linux/kernel/git/mcgrof/linux-next.git/log...
Luis Chamberlain (12):
LICENSES: Add the copyleft-next-0.3.1 license
testing: use the copyleft-next-0.3.1 SPDX tag
selftests: add tests_sysfs module
kernfs: add initial failure injection support
test_sysfs: add support to use kernfs failure injection
kernel/module: add documentation for try_module_get()
fs/kernfs/symlink.c: replace S_IRWXUGO with 0777 on
kernfs_create_link()
fs/sysfs/dir.c: replace S_IRWXU|S_IRUGO|S_IXUGO with 0755
sysfs_create_dir_ns()
sysfs: fix deadlock race with module removal
test_sysfs: enable deadlock tests by default
zram: fix crashes with cpu hotplug multistate
zram: use ATTRIBUTE_GROUPS to fix sysfs deadlock module removal
.../fault-injection/fault-injection.rst | 22 +
LICENSES/dual/copyleft-next-0.3.1 | 237 +++
MAINTAINERS | 9 +-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 4 +-
drivers/block/zram/zram_drv.c | 74 +-
fs/kernfs/Makefile | 1 +
fs/kernfs/dir.c | 41 +-
fs/kernfs/failure-injection.c | 91 ++
fs/kernfs/file.c | 20 +-
fs/kernfs/kernfs-internal.h | 73 +
fs/kernfs/symlink.c | 4 +-
fs/sysfs/dir.c | 5 +-
fs/sysfs/file.c | 10 +-
fs/sysfs/group.c | 1 +
include/linux/kernfs.h | 16 +-
include/linux/module.h | 34 +-
include/linux/sysfs.h | 52 +-
kernel/cgroup/cgroup.c | 2 +-
lib/Kconfig.debug | 25 +
lib/Makefile | 1 +
lib/test_kmod.c | 12 +-
lib/test_sysctl.c | 12 +-
lib/test_sysfs.c | 974 ++++++++++++
tools/testing/selftests/kmod/kmod.sh | 13 +-
tools/testing/selftests/sysctl/sysctl.sh | 12 +-
tools/testing/selftests/sysfs/Makefile | 12 +
tools/testing/selftests/sysfs/config | 5 +
tools/testing/selftests/sysfs/sysfs.sh | 1383 +++++++++++++++++
28 files changed, 3048 insertions(+), 97 deletions(-)
create mode 100644 LICENSES/dual/copyleft-next-0.3.1
create mode 100644 fs/kernfs/failure-injection.c
create mode 100644 lib/test_sysfs.c
create mode 100644 tools/testing/selftests/sysfs/Makefile
create mode 100644 tools/testing/selftests/sysfs/config
create mode 100755 tools/testing/selftests/sysfs/sysfs.sh
--
2.30.2
2 years, 7 months
- 1
- 12