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Date: Wed, 18 Feb 2009 14:33:39 +0100
From: Jan Kiszka <jan.kiszka@domain.hid>
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Subject: [Xenomai-help] __ipipe_syscall_root logic (was: BUG fs/buffer.c
 with Linux 2.6.26, 27)
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To: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>, Philippe Gerum <rpm@xenomai.org>
Cc: xenomai-help <xenomai@xenomai.org>, adeos-main <adeos-main@gna.org>

Jan Kiszka wrote:
> ...
> However, let's assumed we entered __ipipe_syscall_root with root domain
> stalled. If we then return from __ipipe_dispatch_event with 0 (=>
> forward this syscall to Linux), we would not call __fixup_if again so
> that the stalled state is kept. Is this a valid scenario for the given
> task, or would this be broken already? At least it looks like the path
> taken here

Could someone explain __ipipe_syscall_root to me? The comment before the
second __fixup_if() does not help me understanding why we only have to
call it when we do not forward the syscall to Linux. In other words,
this version would make more sense to me (32-bit variant, but 64-bit
looks as fishy as its little brother):

--- a/arch/x86/kernel/ipipe.c
+++ b/arch/x86/kernel/ipipe.c
@@ -540,6 +540,7 @@ asmlinkage void __ipipe_unstall_iret_roo
 asmlinkage int __ipipe_syscall_root(struct pt_regs regs)
 {
 	unsigned long flags;
+	int pass;
 
 	__fixup_if(&regs);
 
@@ -551,8 +552,9 @@ asmlinkage int __ipipe_syscall_root(stru
 	   tail work has to be performed (for handling signals etc). */
 
 	if (__ipipe_syscall_watched_p(current, regs.orig_ax) &&
-	    __ipipe_event_monitored_p(IPIPE_EVENT_SYSCALL) &&
-	    __ipipe_dispatch_event(IPIPE_EVENT_SYSCALL,&regs) > 0) {
+	    __ipipe_event_monitored_p(IPIPE_EVENT_SYSCALL)) {
+		pass = !__ipipe_dispatch_event(IPIPE_EVENT_SYSCALL,&regs);
+
 		/* We might enter here over a non-root domain and exit
 		 * over the root one as a result of the syscall
 		 * (i.e. by recycling the register set of the current
@@ -562,6 +564,9 @@ asmlinkage int __ipipe_syscall_root(stru
 		 * stall bit on exit. */
 		__fixup_if(&regs);
 
+		if (pass)
+			return 0;
+
 		if (ipipe_root_domain_p && !in_atomic()) {
 			/* Sync pending VIRQs before _TIF_NEED_RESCHED is tested. */
 			local_irq_save_hw(flags);

-- 
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