On Tue, 2019-01-29 at 05:46 +0000, Christopher Lameter wrote: > On Mon, 28 Jan 2019, Andrew Morton wrote: > > > > When debugging slab errors in slub.c, sometimes we have to trigger > > > a panic in order to get the coredump file. Add a debug option > > > SLAB_WARN_ON_ERROR to toggle WARN_ON() when the option is set. > > > > > > Change since v1: > > > 1. Add a special debug option SLAB_WARN_ON_ERROR and toggle WARN_ON() > > > if it is set. > > > 2. SLAB_WARN_ON_ERROR can be set by kernel parameter slub_debug. > > > > > > > Hopefully the slab developers will have an opinion on this. > > Debugging slab itself is usually done in kvm or some other virtualized > environment. Then gdb can be used to set breakpoints. Otherwise one may > add printks and stuff to the allocators to figure out more or use perf. > > > What you are changing here is the debugging for data corruption within > objects managed by slub or the metadata. Slub currently outputs extensive > data about the metadata corruption (typically caused by a user of > slab allocation) which should allow you to set a proper > breakpoint not in the allocator but in the subsystem where the corruption > occurs. > Thanks for your comments. The real problems the change can help are: a) classic slub issue. e.g., use-after-free, redzone overwritten. It's more efficient to report a issue as soon as slub detects it. (comparing to monitor the log, set a breakpoint, and re-produce the issue). With the coredump file, we can analyze the issue. b) memory corruption issues caused by h/w write. e.g., memory overwritten by a DMA engine. Memory corruptions may or may not related to the slab cache that reports any error. For example: kmalloc-256 or dentry may report the same errors. If we can preserve the the coredump file without any restore/reset processing in slub, we could have more information of this memory corruption. c) memory corruption issues caused by unstable h/w. e.g., bit flipping because of xxxx DRAM die or applying new power settings. It's hard to re-produce this kind of issue and it much easier to tell this kind of issue in the coredump file without any restore/reset processing. Users can set the option by slub_debug. We can still have the original behavior(keep the system alive) if the option is not set. We can turn on the option when we need the coredump file. (with panic_on_warn is set, of course).
