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@collabora.com Signed-off-by: André Almeida <andrealmeid@collabora.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Cc: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>alistair/sunxi64-5.4-dsi
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@ -2,8 +2,8 @@ Kernel Memory Leak Detector
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===========================
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===========================
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Kmemleak provides a way of detecting possible kernel memory leaks in a
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Kmemleak provides a way of detecting possible kernel memory leaks in a
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way similar to a tracing garbage collector
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way similar to a `tracing garbage collector
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(https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29#Tracing_garbage_collectors),
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<https://en.wikipedia.org/wiki/Tracing_garbage_collection>`_,
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with the difference that the orphan objects are not freed but only
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with the difference that the orphan objects are not freed but only
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reported via /sys/kernel/debug/kmemleak. A similar method is used by the
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reported via /sys/kernel/debug/kmemleak. A similar method is used by the
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Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in
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Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in
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@ -15,10 +15,13 @@ Usage
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CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel
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CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel
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thread scans the memory every 10 minutes (by default) and prints the
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thread scans the memory every 10 minutes (by default) and prints the
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number of new unreferenced objects found. To display the details of all
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number of new unreferenced objects found. If the ``debugfs`` isn't already
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the possible memory leaks::
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mounted, mount with::
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# mount -t debugfs nodev /sys/kernel/debug/
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# mount -t debugfs nodev /sys/kernel/debug/
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To display the details of all the possible scanned memory leaks::
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# cat /sys/kernel/debug/kmemleak
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# cat /sys/kernel/debug/kmemleak
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To trigger an intermediate memory scan::
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To trigger an intermediate memory scan::
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@ -72,6 +75,9 @@ If CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF are enabled, the kmemleak is
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disabled by default. Passing ``kmemleak=on`` on the kernel command
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disabled by default. Passing ``kmemleak=on`` on the kernel command
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line enables the function.
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line enables the function.
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If you are getting errors like "Error while writing to stdout" or "write_loop:
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Invalid argument", make sure kmemleak is properly enabled.
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Basic Algorithm
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Basic Algorithm
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---------------
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---------------
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@ -218,3 +224,37 @@ the pointer is calculated by other methods than the usual container_of
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macro or the pointer is stored in a location not scanned by kmemleak.
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macro or the pointer is stored in a location not scanned by kmemleak.
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Page allocations and ioremap are not tracked.
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Page allocations and ioremap are not tracked.
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Testing with kmemleak-test
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--------------------------
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To check if you have all set up to use kmemleak, you can use the kmemleak-test
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module, a module that deliberately leaks memory. Set CONFIG_DEBUG_KMEMLEAK_TEST
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as module (it can't be used as bult-in) and boot the kernel with kmemleak
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enabled. Load the module and perform a scan with::
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# modprobe kmemleak-test
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# echo scan > /sys/kernel/debug/kmemleak
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Note that the you may not get results instantly or on the first scanning. When
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kmemleak gets results, it'll log ``kmemleak: <count of leaks> new suspected
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memory leaks``. Then read the file to see then::
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# cat /sys/kernel/debug/kmemleak
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unreferenced object 0xffff89862ca702e8 (size 32):
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comm "modprobe", pid 2088, jiffies 4294680594 (age 375.486s)
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hex dump (first 32 bytes):
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6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk
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6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk.
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backtrace:
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[<00000000e0a73ec7>] 0xffffffffc01d2036
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[<000000000c5d2a46>] do_one_initcall+0x41/0x1df
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[<0000000046db7e0a>] do_init_module+0x55/0x200
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[<00000000542b9814>] load_module+0x203c/0x2480
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[<00000000c2850256>] __do_sys_finit_module+0xba/0xe0
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[<000000006564e7ef>] do_syscall_64+0x43/0x110
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[<000000007c873fa6>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
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...
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Removing the module with ``rmmod kmemleak_test`` should also trigger some
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kmemleak results.
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