| Message ID | 20210810051602.3067384-1-mcgrof@kernel.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | kmod: add patient module removal support | expand |
*Friendly poke* Luis
On Wed, Sep 15, 2021 at 10:41 AM Luis Chamberlain <mcgrof@kernel.org> wrote: > > *Friendly poke* Sorry for the delay. Let me take a look in detail tomorrow. Lucas De Marchi > > Luis
On Mon, Sep 20, 2021 at 10:51:46PM -0700, Lucas De Marchi wrote: > On Wed, Sep 15, 2021 at 10:41 AM Luis Chamberlain <mcgrof@kernel.org> wrote: > > > > *Friendly poke* > > Sorry for the delay. Let me take a look in detail tomorrow. *Friendly poke* Luis
On Thu, Feb 17, 2022 at 12:13:01AM -0800, Luis Chamberlain wrote: >On Mon, Sep 20, 2021 at 10:51:46PM -0700, Lucas De Marchi wrote: >> On Wed, Sep 15, 2021 at 10:41 AM Luis Chamberlain <mcgrof@kernel.org> wrote: >> > >> > *Friendly poke* >> >> Sorry for the delay. Let me take a look in detail tomorrow. > >*Friendly poke* oh, I dropped the ball here, sorry. Then I got busy with i915 and other projects. Let me take a look again at your implementation and respin it Lucas De Marchi > > Luis
The kernel used to have wait support for delete_module() system call. This was removed via commmit 3f2b9c9cdf389e ("module: remove rmmod --wait option.") on v3.13 in favor for 10 second sleep on kmod. Lucas later remove that sleep(10) on kmod commit 017893f244 ("rmmod: remove --wait option") so on kmod 16. There are races in module removal I have been chasing down and clearly documenting them. Module removal is not crazy stuff, its used in many test frameworks such as fstests and blktests and can even be used to remove live patches if a distribution supports that. If you are doing tests in a loop you can easily run into these races as false positives in your testing results. Contrary to the last kernel wait delete_module() effort this series instead adds a patient module removal support into kmod and extends modprobe and rmmod to use it. The most important change other than the requested during patch review this also now uses the same timeout to also re-try module removal if it fails when patient module removal is used. Changes on v2: - replace looking at the refcnt with poll() as requested by Lucas. This uses clock_gettime(CLOCK_MONOTONIC), and systems without that won't get patient module removal support, we'd revert back to regular module removal attempt support. Since poll() in practice just busy loops on the refcnt sysfs file today, we guard verbose prints to only every 1/2 second. We can enhance poll() on the refcnt later, for now this busy read helps prove the issue and test for it. - replaces the sleep(1) calls and make thie programmable timeouts as requested by Lucas - extends macros to allow us to print something *more* on the library when something like modprobe -v is used. - upon further testing and investigation of the refcnt issue where the refcnt is 0 but the module cannot be removed [0] I've determined that the only reasonable thing userspace can do is to retry the delete_modue() call when doing a patient removal. You *might* be tempted to look at this and suggest a new quiesce state which userspace can request, however such quiesce states could actually prove more problemantic than resolve anything. Consider how some subystems may need to re-open a device only to close it when tearing something down. Such quiesce efforts would break those subsystems. [0] https://bugzilla.kernel.org/show_bug.cgi?id=214015 Luis Chamberlain (3): libkmod: add a library notice log level print libkmod/libkmod-module: add refcnt fd helper libkmod-module: add support for a patient module removal option libkmod/docs/libkmod-sections.txt | 4 + libkmod/libkmod-internal.h | 2 + libkmod/libkmod-module.c | 365 ++++++++++++++++++++++++++++- libkmod/libkmod.c | 71 ++++++ libkmod/libkmod.h | 7 + libkmod/libkmod.sym | 4 + libkmod/python/kmod/_libkmod_h.pxd | 3 + libkmod/python/kmod/module.pyx | 4 + man/modprobe.xml | 59 +++++ man/rmmod.xml | 60 +++++ tools/modprobe.c | 21 +- tools/remove.c | 12 +- tools/rmmod.c | 27 ++- 13 files changed, 610 insertions(+), 29 deletions(-)