From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jes Sorensen Date: Fri, 31 Mar 2006 16:18:57 +0000 Subject: Re: [patch] avoid unaligned access when accessing poll stack Message-Id: List-Id: References: <200603311800.19364.ak@suse.de> In-Reply-To: <200603311800.19364.ak@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andi Kleen Cc: Linus Torvalds , Andrew Morton , linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org >>>>> "Andi" = Andi Kleen writes: Andi> On Friday 31 March 2006 17:38, Jes Sorensen wrote: >> Hi, >> >> Patch 70674f95c0a2ea694d5c39f4e514f538a09be36f [PATCH] Optimize >> select/poll by putting small data sets on the stack resulted in the >> poll stack being 4-byte aligned on 64-bit architectures, causing >> misaligned accesses to elements in the array. >> >> This patch fixes it by declaring the stack in terms of 'long' >> instead of 'char'. Andi> You should do that for poll too then. I assume you mean select(). Updated patch attached. Jes Force alignment of poll and select stacks to long to avoid unaligned access on 64 bit architectures. Signed-off-by: Jes Sorensen --- fs/select.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) Index: linux-2.6/fs/select.c =================================--- linux-2.6.orig/fs/select.c +++ linux-2.6/fs/select.c @@ -314,7 +314,7 @@ int ret, size, max_fdset; struct fdtable *fdt; /* Allocate small arguments on the stack to save memory and be faster */ - char stack_fds[SELECT_STACK_ALLOC]; + long stack_fds[SELECT_STACK_ALLOC/sizeof(long)]; ret = -EINVAL; if (n < 0) @@ -639,8 +639,10 @@ struct poll_list *walk; struct fdtable *fdt; int max_fdset; - /* Allocate small arguments on the stack to save memory and be faster */ - char stack_pps[POLL_STACK_ALLOC]; + /* Allocate small arguments on the stack to save memory and be + faster - use long to make sure the buffer is aligned properly + on 64 bit archs to avoid unaligned access */ + long stack_pps[POLL_STACK_ALLOC/sizeof(long)]; struct poll_list *stack_pp = NULL; /* Do a sanity check on nfds ... */