From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jack Steiner Date: Thu, 15 Dec 2005 18:41:22 +0000 Subject: Re: [PATCH] - Missed TLB flush Message-Id: <20051215184121.GA20289@sgi.com> List-Id: References: <20051215174525.GA28885@sgi.com> In-Reply-To: <20051215174525.GA28885@sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org Second try. I see why the problem exists only on SN. SN uses a different hardware mechanism to purge TLB entries across nodes. The first part of the patch can be skipped. It looks like there is a bug in the SN TLB flushing code. During context switch, kernel threads inherit the mm of the task that was previously running on the cpu. This confuses the code in sn2_global_tlb_purge(). The result is a missed TLB purge for the task that owns the "borrowed" mm. (I hit the problem running heavy stress where kswapd was purging code pages of a user task that woke kswapd. The user task took a SIGILL fault trying to execute code in the page that had been ripped out from underneath it). Signed-off-by: Jack Steiner Index: linux/arch/ia64/sn/kernel/sn2/sn2_smp.c =================================--- linux.orig/arch/ia64/sn/kernel/sn2/sn2_smp.c 2005-12-15 11:20:49.192339703 -0600 +++ linux/arch/ia64/sn/kernel/sn2/sn2_smp.c 2005-12-15 11:33:28.163678685 -0600 @@ -202,7 +202,7 @@ sn2_global_tlb_purge(struct mm_struct *m unsigned long end, unsigned long nbits) { int i, opt, shub1, cnode, mynasid, cpu, lcpu = 0, nasid, flushed = 0; - int mymm = (mm = current->active_mm); + int mymm = (mm = current->active_mm && current->mm); volatile unsigned long *ptc0, *ptc1; unsigned long itc, itc2, flags, data0 = 0, data1 = 0, rr_value; short nasids[MAX_NUMNODES], nix;