Messages in this thread | | | From | "Eric W. Biederman" <> | Date | Mon, 04 Apr 2022 09:29:10 -0500 | Subject | Re: [PATCH] signal/x86: Delay calling signals in atomic |
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Sebastian Andrzej Siewior <bigeasy@linutronix.de> writes:
> On 2022-03-30 13:10:05 [-0500], Eric W. Biederman wrote: >> But it looks like if we are coming from userspace then we use the same >> stack as any other time we would come from userspace. AKA a stack >> that allows the kernel to sleep. >> >> So I don't see what the problem is that is trying to be fixed. > > It is not only the stack. In atomic context / disabled interrupts it is > not possible to acquire a spinlock_t (sighand_struct::siglock) which is > done later.
Looking at do_int3_user the interrupts must be enabled. > >> I know that code has been changed over the years, perhaps this is >> something that was fixed upstream and the real time tree didn't realize >> there was no longer a need to fix anything? >> >> Or am I missing something subtle when reading the idtentry assembly? > > It certainly is true that the code changed over the years. The per-CPU > stack is one problem, the siglock in atomic context is the other one. > Thank you for the input. Let me digest the informations I have here and > get back.
Certainly. I case it helps this is the relevant bit of code:
static void do_int3_user(struct pt_regs *regs) { if (do_int3(regs)) return;
cond_local_irq_enable(regs); do_trap(X86_TRAP_BP, SIGTRAP, "int3", regs, 0, 0, NULL); cond_local_irq_disable(regs); }
The signal delivery where siglock is take happens inside of do_trap. If we are coming from kernel mode only do_int3 is called.
Coming from user_mode we switch to the task stack and enable interrupts.
Unless I am misreading the code the cond_local_irq_{enable/disable} can correctly be replaced local_irq_{enable/disable} as coming from user mode interrupts are always enabled.
Unless I am misreading cond_local_irq_enable. If for some reason cond_local_irq_enable doesn't enable interrupts when come from user mode fixing that appears to be the fix that is needed.
Eric
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