[PATCH V2] powerpc/fscr: Enable interrupts earlier before calling get_user()

[PATCH V2] powerpc/fscr: Enable interrupts earlier before calling get_user()

[Anshuman Khandual]

The function get_user() can sleep while trying to fetch instruction
from user address space and causes the following warning from the
scheduler.

BUG: sleeping function called from invalid context

Though interrupts get enabled back but it happens bit later after
get_user() is called. This change moves enabling these interrupts
earlier covering the function get_user(). While at this, lets check
for kernel mode and crash as this interrupt should not have been
triggered from the kernel context.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
---
Changes in V2:
- Moved facility string detection earlier in the function
- Used pr_emerg() and die() instead of BUG_ON() if kernel context
- Removed redundant user_mode() check at the end

 arch/powerpc/kernel/traps.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
index 1e48d15..317593d 100644
--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1612,6 +1612,22 @@ void facility_unavailable_exception(struct pt_regs *regs)
 		value = mfspr(SPRN_FSCR);
 
 	status = value >> 56;
+	if ((hv || status >= 2) &&
+	    (status < ARRAY_SIZE(facility_strings)) &&
+	    facility_strings[status])
+		facility = facility_strings[status];
+
+	/* We should not have taken this interrupt in kernel */
+	if (!user_mode(regs)) {
+		pr_emerg("Facility '%s' unavailable (%d) exception in kernel"
+		       " mode at %lx\n", facility, status, regs->nip);
+		die("Unexpected facility unavailable exception", regs, SIGABRT);
+	}
+
+	/* We restore the interrupt state now */
+	if (!arch_irq_disabled_regs(regs))
+		local_irq_enable();
+
 	if (status == FSCR_DSCR_LG) {
 		/*
 		 * User is accessing the DSCR register using the problem
@@ -1678,25 +1694,11 @@ void facility_unavailable_exception(struct pt_regs *regs)
 		return;
 	}
 
-	if ((hv || status >= 2) &&
-	    (status < ARRAY_SIZE(facility_strings)) &&
-	    facility_strings[status])
-		facility = facility_strings[status];
-
-	/* We restore the interrupt state now */
-	if (!arch_irq_disabled_regs(regs))
-		local_irq_enable();
-
 	pr_err_ratelimited("%sFacility '%s' unavailable (%d), exception at 0x%lx, MSR=%lx\n",
 		hv ? "Hypervisor " : "", facility, status, regs->nip, regs->msr);
 
 out:
-	if (user_mode(regs)) {
-		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
-		return;
-	}
-
-	die("Unexpected facility unavailable exception", regs, SIGABRT);
+	_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
 }
 #endif
 
-- 
1.8.3.1

Re: [V2] powerpc/fscr: Enable interrupts earlier before calling get_user()

[Michael Ellerman]

On Thu, 2018-03-29 at 06:23:37 UTC, Anshuman Khandual wrote:
> The function get_user() can sleep while trying to fetch instruction
> from user address space and causes the following warning from the
> scheduler.
> 
> BUG: sleeping function called from invalid context
> 
> Though interrupts get enabled back but it happens bit later after
> get_user() is called. This change moves enabling these interrupts
> earlier covering the function get_user(). While at this, lets check
> for kernel mode and crash as this interrupt should not have been
> triggered from the kernel context.
> 
> Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/709b973c844c0b4d115ac3a227a2e5

cheers