Hello, I manage to have more information about the issue by the use of
strace, the blocking call is an ioctl on /dev/mapper/control:
write(1, "# dm versions [ opencount flus"..., 51# dm versions [
opencount flush ] [16384] (*1)) = 51
ioctl(3, DM_LIST_VERSIONS, {version=4.1.0, data_size=16384,
data_start=312, flags=DM_EXISTS_FLAG} => {version=4.39.0,
data_size=431, data_start=312, flags=DM_EXISTS_FLAG, ...}) = 0
write(1, "# dm remove luksDeviceTest [ op"..., 75# dm remove
luksDeviceTest [ opencount flush retryremove ] [16384] (*1)) = 75
ioctl(3, DM_DEV_REMOVE, {version=4.0.0, data_size=16384,
name="luksDeviceTest", event_nr=4194304, flags=DM_EXISTS_FLAGS}
to be compare to the same call without
7fcfa8b616d360ab9ea1da94c2200f0708e0188b commit:
ioctl(3, DM_LIST_VERSIONS, {version=4.1.0, data_size=16384,
data_start=312, flags=DM_EXISTS_FLAG} => {version=4.39.0,
data_size=431, data_start=312, flags=DM_EXISTS_FLAG, ...}) = 0
write(1, "# dm remove luksDeviceTest [ op"..., 75# dm remove
luksDeviceTest [ opencount flush retryremove ] [16384] (*1)) = 75
ioctl(3, DM_DEV_REMOVE, {version=4.0.0, data_size=16384,
name="luksDeviceTest", event_nr=4194304, flags=DM_EXISTS_FLAG} =>
{version=4.39.0, data_size=305, name="luksDeviceTest",
uuid="CRYPT-LUKS1-25edf7523ab4454590a7e2ac83050582-luksDeviceTest",
flags=DM_EXISTS_FLAG|DM_UEVENT_GENERATED_FLAG}) = 0
write(1, "# luksDeviceTest: Stacking NODE_"..., 36# luksDeviceTest:
Stacking NODE_DEL) = 36
write(1, "# luksDeviceTest: Processing NOD"..., 38# luksDeviceTest:
Processing NODE_DEL) = 38
The matching code line which block is
https://github.com/lvmteam/lvm2/blob/v2_03_06/libdm/ioctl/libdm-iface.c#L1890
I don't know how to go deeper to understand why preempt-rt is blocking
of this, any ideas ?
Another question is about the impact of reverting commit
https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-stable-rt.git/commit/?h=v4.19-rt&id=7fcfa8b616d360ab9ea1da94c2200f0708e0188b
, what are the risk of doing that ?
