mm: call force_sig_info before prints

Started by Maninder Singh on Dec 19, 2016 · 2 messages from 2 authors · Last reply Dec 19, 2016

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STALE3608d REVIEWED · 1 review, 0 by maintainers

Status: Reviewed.

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Message details and related content
prints can delay queuing of signal, so better to print
after force_sig_info.

Let's say process generated SIGSEGV , and some other thread sends
SIGKILL to crashing process and it gets queued before SIGSEGV becuase
of little delay due to prints so in this case coredump might not generate.

Signed-off-by: Maninder Singh <redacted>
Signed-off-by: Amit Nagal <redacted>
Reviewed-by: Ajeet Yadav <redacted>
---
 arch/arm/mm/fault.c   | 18 +++++++++---------
 arch/arm64/mm/fault.c | 16 ++++++++--------
 2 files changed, 17 insertions(+), 17 deletions(-)
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index 3a2e678..f92f90b 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -163,6 +163,15 @@ void show_pte(struct mm_struct *mm, unsigned long addr)
 {
 	struct siginfo si;
 
+	tsk->thread.address = addr;
+	tsk->thread.error_code = fsr;
+	tsk->thread.trap_no = 14;
+	si.si_signo = sig;
+	si.si_errno = 0;
+	si.si_code = code;
+	si.si_addr = (void __user *)addr;
+	force_sig_info(sig, &si, tsk);
+
 #ifdef CONFIG_DEBUG_USER
 	if (((user_debug & UDBG_SEGV) && (sig == SIGSEGV)) ||
 	    ((user_debug & UDBG_BUS)  && (sig == SIGBUS))) {
@@ -172,15 +181,6 @@ void show_pte(struct mm_struct *mm, unsigned long addr)
 		show_regs(regs);
 	}
 #endif
-
-	tsk->thread.address = addr;
-	tsk->thread.error_code = fsr;
-	tsk->thread.trap_no = 14;
-	si.si_signo = sig;
-	si.si_errno = 0;
-	si.si_code = code;
-	si.si_addr = (void __user *)addr;
-	force_sig_info(sig, &si, tsk);
 }
 
 void do_bad_area(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index a78a5c4..eb5d0e3 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -197,14 +197,6 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 {
 	struct siginfo si;
 
-	if (unhandled_signal(tsk, sig) && show_unhandled_signals_ratelimited()) {
-		pr_info("%s[%d]: unhandled %s (%d) at 0x%08lx, esr 0x%03x\n",
-			tsk->comm, task_pid_nr(tsk), fault_name(esr), sig,
-			addr, esr);
-		show_pte(tsk->mm, addr);
-		show_regs(regs);
-	}
-
 	tsk->thread.fault_address = addr;
 	tsk->thread.fault_code = esr;
 	si.si_signo = sig;
@@ -212,6 +204,14 @@ static void __do_user_fault(struct task_struct *tsk, unsigned long addr,
 	si.si_code = code;
 	si.si_addr = (void __user *)addr;
 	force_sig_info(sig, &si, tsk);
+
+	if (unhandled_signal(tsk, sig) && show_unhandled_signals_ratelimited()) {
+		pr_info("%s[%d]: unhandled %s (%d) at 0x%08lx, esr 0x%03x\n",
+			tsk->comm, task_pid_nr(tsk), fault_name(esr), sig,
+			addr, esr);
+		show_pte(tsk->mm, addr);
+		show_regs(regs);
+	}
 }
 
 static void do_bad_area(unsigned long addr, unsigned int esr, struct pt_regs *regs)
-- 
1.9.1
Message details and related content
On Mon, Dec 19, 2016 at 04:07:12PM +0530, Maninder Singh wrote:
prints can delay queuing of signal, so better to print
after force_sig_info.

Let's say process generated SIGSEGV , and some other thread sends
SIGKILL to crashing process and it gets queued before SIGSEGV becuase
of little delay due to prints so in this case coredump might not generate.
In any case, that's going to be a race - you can't predict exactly when
the "other thread" will send the SIGKILL in relation to the SIGSEGV.

So, I don't see the point of this change.

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