diff options
Diffstat (limited to 'kernel/module/Kconfig')
| -rw-r--r-- | kernel/module/Kconfig | 59 |
1 files changed, 59 insertions, 0 deletions
diff --git a/kernel/module/Kconfig b/kernel/module/Kconfig index e6df183e2c80..33a2e991f608 100644 --- a/kernel/module/Kconfig +++ b/kernel/module/Kconfig @@ -59,6 +59,65 @@ config MODULE_STATS If unsure, say N. +config MODULE_DEBUG_AUTOLOAD_DUPS + bool "Debug duplicate modules with auto-loading" + help + Module autoloading allows in-kernel code to request modules through + the *request_module*() API calls. This in turn just calls userspace + modprobe. Although modprobe checks to see if a module is already + loaded before trying to load a module there is a small time window in + which multiple duplicate requests can end up in userspace and multiple + modprobe calls race calling finit_module() around the same time for + duplicate modules. The finit_module() system call can consume in the + worst case more than twice the respective module size in virtual + memory for each duplicate module requests. Although duplicate module + requests are non-fatal virtual memory is a limited resource and each + duplicate module request ends up just unnecessarily straining virtual + memory. + + This debugging facility will create pr_warn() splats for duplicate + module requests to help identify if module auto-loading may be the + culprit to your early boot virtual memory pressure. Since virtual + memory abuse caused by duplicate module requests could render a + system unusable this functionality will also converge races in + requests for the same module to a single request. You can boot with + the module.enable_dups_trace=1 kernel parameter to use WARN_ON() + instead of the pr_warn(). + + If the first module request used request_module_nowait() we cannot + use that as the anchor to wait for duplicate module requests, since + users of request_module() do want a proper return value. If a call + for the same module happened earlier with request_module() though, + then a duplicate request_module_nowait() would be detected. The + non-wait request_module() call is synchronous and waits until modprobe + completes. Subsequent auto-loading requests for the same module do + not trigger a new finit_module() calls and do not strain virtual + memory, and so as soon as modprobe successfully completes we remove + tracking for duplicates for that module. + + Enable this functionality to try to debug virtual memory abuse during + boot on systems which are failing to boot or if you suspect you may be + straining virtual memory during boot, and you want to identify if the + abuse was due to module auto-loading. These issues are currently only + known to occur on systems with many CPUs (over 400) and is likely the + result of udev issuing duplicate module requests for each CPU, and so + module auto-loading is not the culprit. There may very well still be + many duplicate module auto-loading requests which could be optimized + for and this debugging facility can be used to help identify them. + + Only enable this for debugging system functionality, never have it + enabled on real systems. + +config MODULE_DEBUG_AUTOLOAD_DUPS_TRACE + bool "Force full stack trace when duplicates are found" + depends on MODULE_DEBUG_AUTOLOAD_DUPS + help + Enabling this will force a full stack trace for duplicate module + auto-loading requests using WARN_ON() instead of pr_warn(). You + should keep this disabled at all times unless you are a developer + and are doing a manual inspection and want to debug exactly why + these duplicates occur. + endif # MODULE_DEBUG config MODULE_FORCE_LOAD |