Re: [PATCH 2/22] use_mm fix (helps AIO hangs on 4:4 split)

[Suparna Bhattacharya]

On Fri, Jul 02, 2004 at 06:30:30PM +0530, Suparna Bhattacharya wrote:
> The patchset contains modifications and fixes to the AIO core
> to support the full retry model, an implementation of AIO
> support for buffered filesystem AIO reads and O_SYNC writes
> (the latter courtesy O_SYNC speedup changes from Andrew Morton),
> an implementation of AIO reads and writes to pipes (from
> Chris Mason) and AIO poll (again from Chris Mason).
> 
> Full retry infrastructure and fixes
> [1] aio-retry.patch
> [2] 4g4g-aio-hang-fix.patch

As Christoph Hellwig pointed out, though the problem originally
surfaced as hangs with retry and 4G-4G, the fixes here are generic
and apply irrespective of 4:4.

-- 
Suparna Bhattacharya (suparna@xxxxxxxxxx)
Linux Technology Center
IBM Software Lab, India

--------------------------------------------
From: Suparna Bhattacharya <suparna@xxxxxxxxxx>

This patch appears to fix the hangs seen with AIO and 4G-4G for me.  It
ensures that the indirect versions of copy_xxx_user are used during aio
retries running in worker thread context (i.e.  access aio issuer's
user-space instead of kernel-space).


 fs/aio.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletion(-)

--- aio/fs/aio.c	2004-06-17 10:58:34.596512112 -0700
+++ 4g4g-aio-hang-fix/fs/aio.c	2004-06-17 12:29:35.380346784 -0700
@@ -795,18 +795,23 @@ static inline void aio_run_iocbs(struct 
  * aio_kick_handler:
  * 	Work queue handler triggered to process pending
  * 	retries on an ioctx. Takes on the aio issuer's
- * 	mm context before running the iocbs.
+ *	mm context before running the iocbs, so that
+ *	copy_xxx_user operates on the issuer's address
+ *      space.
  * Run on aiod's context.
  */
 static void aio_kick_handler(void *data)
 {
 	struct kioctx *ctx = data;
+	mm_segment_t oldfs = get_fs();
 
+	set_fs(USER_DS);
 	use_mm(ctx->mm);
 	spin_lock_irq(&ctx->ctx_lock);
 	__aio_run_iocbs(ctx);
  	unuse_mm(ctx->mm);
 	spin_unlock_irq(&ctx->ctx_lock);
+	set_fs(oldfs);
 }
  
 
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