FAILED: patch "[PATCH] riscv: fix a nasty sigreturn bug..." failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

Possible dependencies:

762df359aa58 ("riscv: fix a nasty sigreturn bug...")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 762df359aa5849e010ef04c3ed79d57588ce17d9 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Fri, 24 Sep 2021 01:55:27 +0000
Subject: [PATCH] riscv: fix a nasty sigreturn bug...

riscv has an equivalent of arm bug fixed by 653d48b22166 ("arm: fix
really nasty sigreturn bug"); if signal gets caught by an interrupt that
hits when we have the right value in a0 (-513), *and* another signal
gets delivered upon sigreturn() (e.g. included into the blocked mask for
the first signal and posted while the handler had been running), the
syscall restart logics will see regs->cause equal to EXC_SYSCALL (we are
in a syscall, after all) and a0 already restored to its original value
(-513, which happens to be -ERESTARTNOINTR) and assume that we need to
apply the usual syscall restart logics.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Fixes: e2c0cdfba7f6 ("RISC-V: User-facing API")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/YxJEiSq%2FCGaL6Gm9@ZenIV/
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 5a2de6b6f882..5c591123c440 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -124,6 +124,8 @@ SYSCALL_DEFINE0(rt_sigreturn)
 	if (restore_altstack(&frame->uc.uc_stack))
 		goto badframe;
 
+	regs->cause = -1UL;
+
 	return regs->a0;
 
 badframe: