Linux thread kernel stack size
![linux thread kernel stack size linux thread kernel stack size](https://i.stack.imgur.com/WL9It.png)
There is one "kernel stack" per CPU like ISR Stack and one "kernel stack" per Process. Suppose you keep same stack for both kernel & user space, then simple segfault in user application crashes kernel and needs restart. What's the difference between kernel stack and user stack?Īs a kernel programmer, you know that the kernel should be restricted from erroneous user programs. My answer is collected from other SO questions with my stuffs. but this is digressing a bit from the original question. There are multiple ways for this: UNIX signals, setcontext(), pthread_yield() / pthread_cancel(). That said, the process can influence scheduling of its threads and/or influence the context (state, amongst that is the thread's stack pointer). As threads are created (and each process must have at least one thread), the kernel creates kernel stacks for them, while user space stacks are either explicitly created/provided by whichever mechanism is used to create a thread (functions like makecontext() or pthread_create() allow the caller to specify a memory region to be used for the "child" thread's stack), or inherited (by on-access memory cloning, usually called "copy on write" / COW, when creating a new process). Scheduling (how / when different threads are being run, how their state is saved and restored) is the operating system's task and processes don't need to concern themselves with this. How does the process coordinate between both these stacks ?.Remember the only difference between processes and threads (to Linux) is the fact that multiple threads can share an address space (forming a process). Not just each process - each thread has its own kernel stack (and, in fact, its own user stack as well). Does each process have its own kernel stack ?.solution is to increase kernel stack sizes for such workloads).
![linux thread kernel stack size linux thread kernel stack size](https://mcuoneclipse.files.wordpress.com/2018/05/freertos-task-stack-information-with-configrecord_stack_high_address.png)
Linux thread kernel stack size software#
This can, if interrupt handlers have deeply nested call paths, lead to stack overflows (if a deep kernel call path is interrupted and the handler causes another deep path in Linux, filesystem / software RAID code being interrupted by network code with iptables active is known to trigger such in untuned older kernels. That said, interrupts that occur while executing kernel code will simply (continue to) use the kernel stack in place at that point. The CPU itself when dispatching an interrupt might execute a privilege and/or stack switch, and this is used/set up by the kernel so that the common interrupt entry code can already rely on a kernel stack being present. The kernel (Linux kernel, that is) does not hook ISRs directly to the x86 architecture's interrupt gates but instead delegates the interrupt dispatch to a common kernel interrupt entry/exit mechanism which saves pre-interrupt register state before calling the registered handler(s). If a local variable is declared in an ISR, where will it be stored ?.Different CPU architectures implement this in different ways x86 CPUs automatically switch stack pointers when privilege mode switches occur, and the values to be used for different privilege levels are configurable - by privileged code (i.e. The kernel therefore cannot trust the user space stack pointer to be valid nor usable, and therefore will require one set under its own control. For one, user space programs can make their stack (pointer) anything they want, and there is usually no architectural requirement to even have a valid one. Vice versa, without explicitly being requested by the kernel code (in Linux, through functions like copy_from_user()), user memory (including the user stack) is not usually directly accessible.
![linux thread kernel stack size linux thread kernel stack size](https://www.andrew.cmu.edu/course/15-440-sp10/applications/ln/thdcontext.jpg)
when executing in user mode, kernel memory (part of which is the kernel stack) will not be accessible even if mapped.
![linux thread kernel stack size linux thread kernel stack size](https://linux-kernel-labs.github.io/refs/heads/master/_images/ditaa-f6b228332baf165f498d8a1bb0bc0bdb91ae50c5.png)
In short, nothing - apart from using a different location in memory (and hence a different value for the stack pointer register), and usually different memory access protections.