Simplfy the concurrency delimiter we user for kmod with the semaphore.
I had used the kmod strategy to try to implement a similar concurrency
delimiter for the kernel_read*() calls from the finit_module() path
so to reduce vmalloc() memory pressure. That effort didn't provid yet
conclusive results, but one thing that did became clear is we can use
the suggested alternative solution with semaphores which Linus hinted
at instead of using the atomic / wait strategy.
I've stress tested this with kmod test 0008:
time /data/linux-next/tools/testing/selftests/kmod/kmod.sh -t 0008
And I get only a *slight* delay. That delay however is small, a few
seconds for a full test loop run that runs 150 times, for about ~30-40
seconds. The small delay is worth the simplfication IMHO.
Signed-off-by: Luis Chamberlain <[email protected]>
---
kernel/module/kmod.c | 26 +++++++-------------------
1 file changed, 7 insertions(+), 19 deletions(-)
diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c
index b717134ebe17..925eb85b8346 100644
--- a/kernel/module/kmod.c
+++ b/kernel/module/kmod.c
@@ -40,8 +40,7 @@
* effect. Systems like these are very unlikely if modules are enabled.
*/
#define MAX_KMOD_CONCURRENT 50
-static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
-static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
+static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
/*
* This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
@@ -148,29 +147,18 @@ int __request_module(bool wait, const char *fmt, ...)
if (ret)
return ret;
- if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
- pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
- atomic_read(&kmod_concurrent_max),
- MAX_KMOD_CONCURRENT, module_name);
- ret = wait_event_killable_timeout(kmod_wq,
- atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
- MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
- if (!ret) {
- pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
- module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
- return -ETIME;
- } else if (ret == -ERESTARTSYS) {
- pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
- return ret;
- }
+ ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT);
+ if (ret) {
+ pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
+ module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
+ return ret;
}
trace_module_request(module_name, wait, _RET_IP_);
ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
- atomic_inc(&kmod_concurrent_max);
- wake_up(&kmod_wq);
+ up(&kmod_concurrent_max);
return ret;
}
--
2.39.2
In the title: s/sempahore/semaphore
On Wed, 05 Apr 2023, Luis Chamberlain wrote:
>Simplfy the concurrency delimiter we user for kmod with the semaphore.
>I had used the kmod strategy to try to implement a similar concurrency
>delimiter for the kernel_read*() calls from the finit_module() path
>so to reduce vmalloc() memory pressure. That effort didn't provid yet
>conclusive results, but one thing that did became clear is we can use
>the suggested alternative solution with semaphores which Linus hinted
>at instead of using the atomic / wait strategy.
>
>I've stress tested this with kmod test 0008:
>
>time /data/linux-next/tools/testing/selftests/kmod/kmod.sh -t 0008
>
>And I get only a *slight* delay. That delay however is small, a few
>seconds for a full test loop run that runs 150 times, for about ~30-40
>seconds. The small delay is worth the simplfication IMHO.
Yes, code looks a lot nicer.
Reviewed-by: Davidlohr Bueso <[email protected]>
>Signed-off-by: Luis Chamberlain <[email protected]>
>---
> kernel/module/kmod.c | 26 +++++++-------------------
> 1 file changed, 7 insertions(+), 19 deletions(-)
>
>diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c
>index b717134ebe17..925eb85b8346 100644
>--- a/kernel/module/kmod.c
>+++ b/kernel/module/kmod.c
>@@ -40,8 +40,7 @@
> * effect. Systems like these are very unlikely if modules are enabled.
> */
> #define MAX_KMOD_CONCURRENT 50
>-static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
>-static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
>+static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
>
> /*
> * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
>@@ -148,29 +147,18 @@ int __request_module(bool wait, const char *fmt, ...)
> if (ret)
> return ret;
>
>- if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
>- pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
>- atomic_read(&kmod_concurrent_max),
>- MAX_KMOD_CONCURRENT, module_name);
>- ret = wait_event_killable_timeout(kmod_wq,
>- atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
>- MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
>- if (!ret) {
>- pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
>- module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
>- return -ETIME;
>- } else if (ret == -ERESTARTSYS) {
>- pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
>- return ret;
>- }
>+ ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT);
>+ if (ret) {
>+ pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
>+ module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
>+ return ret;
> }
>
> trace_module_request(module_name, wait, _RET_IP_);
>
> ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
>
>- atomic_inc(&kmod_concurrent_max);
>- wake_up(&kmod_wq);
>+ up(&kmod_concurrent_max);
>
> return ret;
> }
>--
>2.39.2
>
On 05.04.23 22:35, Luis Chamberlain wrote:
> Simplfy the concurrency delimiter we user for kmod with the semaphore.
> I had used the kmod strategy to try to implement a similar concurrency
> delimiter for the kernel_read*() calls from the finit_module() path
> so to reduce vmalloc() memory pressure. That effort didn't provid yet
> conclusive results, but one thing that did became clear is we can use
> the suggested alternative solution with semaphores which Linus hinted
> at instead of using the atomic / wait strategy.
>
> I've stress tested this with kmod test 0008:
>
> time /data/linux-next/tools/testing/selftests/kmod/kmod.sh -t 0008
>
> And I get only a *slight* delay. That delay however is small, a few
> seconds for a full test loop run that runs 150 times, for about ~30-40
> seconds. The small delay is worth the simplfication IMHO.
>
> Signed-off-by: Luis Chamberlain <[email protected]>
> ---
> kernel/module/kmod.c | 26 +++++++-------------------
> 1 file changed, 7 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c
> index b717134ebe17..925eb85b8346 100644
> --- a/kernel/module/kmod.c
> +++ b/kernel/module/kmod.c
> @@ -40,8 +40,7 @@
> * effect. Systems like these are very unlikely if modules are enabled.
> */
> #define MAX_KMOD_CONCURRENT 50
> -static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
> -static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
> +static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
>
> /*
> * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
> @@ -148,29 +147,18 @@ int __request_module(bool wait, const char *fmt, ...)
> if (ret)
> return ret;
>
> - if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
> - pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
> - atomic_read(&kmod_concurrent_max),
> - MAX_KMOD_CONCURRENT, module_name);
> - ret = wait_event_killable_timeout(kmod_wq,
> - atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
> - MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
> - if (!ret) {
> - pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
> - module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
> - return -ETIME;
> - } else if (ret == -ERESTARTSYS) {
> - pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
> - return ret;
> - }
> + ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT);
> + if (ret) {
> + pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
> + module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
> + return ret;
> }
>
> trace_module_request(module_name, wait, _RET_IP_);
>
> ret = call_modprobe(module_name, wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
>
> - atomic_inc(&kmod_concurrent_max);
> - wake_up(&kmod_wq);
> + up(&kmod_concurrent_max);
>
> return ret;
> }
Much cleaner
Reviewed-by: David Hildenbrand <[email protected]>
--
Thanks,
David / dhildenb
Hi,
On Wed, 5 Apr 2023, Luis Chamberlain wrote:
s/sempahore/semaphore/ in the subject
> Simplfy the concurrency delimiter we user for kmod with the semaphore.
"Simplify the concurrency delimiter we use for kmod with the semaphore."
(two typos)
> I had used the kmod strategy to try to implement a similar concurrency
> delimiter for the kernel_read*() calls from the finit_module() path
> so to reduce vmalloc() memory pressure. That effort didn't provid yet
s/provid/provide/
> conclusive results, but one thing that did became clear is we can use
s/did // (or s/became/become/)
> the suggested alternative solution with semaphores which Linus hinted
> at instead of using the atomic / wait strategy.
>
> I've stress tested this with kmod test 0008:
>
> time /data/linux-next/tools/testing/selftests/kmod/kmod.sh -t 0008
>
> And I get only a *slight* delay. That delay however is small, a few
> seconds for a full test loop run that runs 150 times, for about ~30-40
> seconds. The small delay is worth the simplfication IMHO.
>
> Signed-off-by: Luis Chamberlain <[email protected]>
> ---
> kernel/module/kmod.c | 26 +++++++-------------------
> 1 file changed, 7 insertions(+), 19 deletions(-)
>
> diff --git a/kernel/module/kmod.c b/kernel/module/kmod.c
> index b717134ebe17..925eb85b8346 100644
> --- a/kernel/module/kmod.c
> +++ b/kernel/module/kmod.c
> @@ -40,8 +40,7 @@
> * effect. Systems like these are very unlikely if modules are enabled.
> */
> #define MAX_KMOD_CONCURRENT 50
> -static atomic_t kmod_concurrent_max = ATOMIC_INIT(MAX_KMOD_CONCURRENT);
> -static DECLARE_WAIT_QUEUE_HEAD(kmod_wq);
> +static DEFINE_SEMAPHORE(kmod_concurrent_max, MAX_KMOD_CONCURRENT);
>
> /*
> * This is a restriction on having *all* MAX_KMOD_CONCURRENT threads
> @@ -148,29 +147,18 @@ int __request_module(bool wait, const char *fmt, ...)
> if (ret)
> return ret;
>
> - if (atomic_dec_if_positive(&kmod_concurrent_max) < 0) {
> - pr_warn_ratelimited("request_module: kmod_concurrent_max (%u) close to 0 (max_modprobes: %u), for module %s, throttling...",
> - atomic_read(&kmod_concurrent_max),
> - MAX_KMOD_CONCURRENT, module_name);
> - ret = wait_event_killable_timeout(kmod_wq,
> - atomic_dec_if_positive(&kmod_concurrent_max) >= 0,
> - MAX_KMOD_ALL_BUSY_TIMEOUT * HZ);
> - if (!ret) {
> - pr_warn_ratelimited("request_module: modprobe %s cannot be processed, kmod busy with %d threads for more than %d seconds now",
> - module_name, MAX_KMOD_CONCURRENT, MAX_KMOD_ALL_BUSY_TIMEOUT);
> - return -ETIME;
> - } else if (ret == -ERESTARTSYS) {
> - pr_warn_ratelimited("request_module: sigkill sent for modprobe %s, giving up", module_name);
> - return ret;
> - }
> + ret = down_timeout(&kmod_concurrent_max, MAX_KMOD_ALL_BUSY_TIMEOUT);
MAX_KMOD_ALL_BUSY_TIMEOUT * HZ ?
The simplification is very nice.
Miroslav
On Thu, Apr 13, 2023 at 11:44:51AM +0200, Miroslav Benes wrote:
> Hi,
<spell checks>
Thanks, fixed!
> MAX_KMOD_ALL_BUSY_TIMEOUT * HZ ?
Yes! In the end schedule_timeout() is used so yup, thanks!
Luis