From: André Almeida <andrealmeid@xxxxxxxxxxxxx> Subject: docs: kmemleak: add more documentation details Wikipedia now has a main article to "tracing garbage collector" topic. Change the URL and use the reStructuredText syntax for hyperlinks and add more details about the use of the tool. Add a section about how to use the kmemleak-test module to test the memory leak scanning. Link: http://lkml.kernel.org/r/20190612155231.19448-2-andrealmeid@xxxxxxxxxxxxx Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxxxxx> Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- Documentation/dev-tools/kmemleak.rst | 48 ++++++++++++++++++++++--- 1 file changed, 44 insertions(+), 4 deletions(-) --- a/Documentation/dev-tools/kmemleak.rst~docs-kmemleak-add-more-documentation-details +++ a/Documentation/dev-tools/kmemleak.rst @@ -2,8 +2,8 @@ Kernel Memory Leak Detector =========================== Kmemleak provides a way of detecting possible kernel memory leaks in a -way similar to a tracing garbage collector -(https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29#Tracing_garbage_collectors), +way similar to a `tracing garbage collector +<https://en.wikipedia.org/wiki/Tracing_garbage_collection>`_, with the difference that the orphan objects are not freed but only reported via /sys/kernel/debug/kmemleak. A similar method is used by the Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in @@ -15,10 +15,13 @@ Usage CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel thread scans the memory every 10 minutes (by default) and prints the -number of new unreferenced objects found. To display the details of all -the possible memory leaks:: +number of new unreferenced objects found. If the ``debugfs`` isn't already +mounted, mount with:: # mount -t debugfs nodev /sys/kernel/debug/ + +To display the details of all the possible scanned memory leaks:: + # cat /sys/kernel/debug/kmemleak To trigger an intermediate memory scan:: @@ -72,6 +75,9 @@ If CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF are disabled by default. Passing ``kmemleak=on`` on the kernel command line enables the function. +If you are getting errors like "Error while writing to stdout" or "write_loop: +Invalid argument", make sure kmemleak is properly enabled. + Basic Algorithm --------------- @@ -218,3 +224,37 @@ the pointer is calculated by other metho macro or the pointer is stored in a location not scanned by kmemleak. Page allocations and ioremap are not tracked. + +Testing with kmemleak-test +-------------------------- + +To check if you have all set up to use kmemleak, you can use the kmemleak-test +module, a module that deliberately leaks memory. Set CONFIG_DEBUG_KMEMLEAK_TEST +as module (it can't be used as bult-in) and boot the kernel with kmemleak +enabled. Load the module and perform a scan with:: + + # modprobe kmemleak-test + # echo scan > /sys/kernel/debug/kmemleak + +Note that the you may not get results instantly or on the first scanning. When +kmemleak gets results, it'll log ``kmemleak: <count of leaks> new suspected +memory leaks``. Then read the file to see then:: + + # cat /sys/kernel/debug/kmemleak + unreferenced object 0xffff89862ca702e8 (size 32): + comm "modprobe", pid 2088, jiffies 4294680594 (age 375.486s) + hex dump (first 32 bytes): + 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk + 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk. + backtrace: + [<00000000e0a73ec7>] 0xffffffffc01d2036 + [<000000000c5d2a46>] do_one_initcall+0x41/0x1df + [<0000000046db7e0a>] do_init_module+0x55/0x200 + [<00000000542b9814>] load_module+0x203c/0x2480 + [<00000000c2850256>] __do_sys_finit_module+0xba/0xe0 + [<000000006564e7ef>] do_syscall_64+0x43/0x110 + [<000000007c873fa6>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 + ... + +Removing the module with ``rmmod kmemleak_test`` should also trigger some +kmemleak results. _
