Hi
This patch avoids a possible deadlock in dm-bufio. (it could happen only
with large block size, at most PAGE_SIZE << MAX_ORDER (typically 8MiB).
Mikulas
---
dm-bufio: use memalloc_noio_save()
__vmalloc doesn't fully respect gfp flags. The specified gfp flags are
used for allocation of requested pages, structures vmap_area, vmap_block
and vm_struct and the radix tree nodes.
However, the kernel pagetables are allocated always with GFP_KERNEL. Thus
the allocation of pagetables can recurse back to the I/O layer and cause a
deadlock.
This patch uses the function memalloc_noio_save to set per-process
PF_MEMALLOC_NOIO flag and the function memalloc_noio_restore to restore
it. When this flag is set, all allocations in the process are done with
implied GFP_NOIO flag, thus the deadlock can't happen.
This should be backported to stable kernels, but they don't have the
PF_MEMALLOC_NOIO flag and memalloc_noio_save/memalloc_noio_restore
functions. So, PF_MEMALLOC should be set and restored instead.
Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
drivers/md/dm-bufio.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
Index: linux-3.9-rc5-fast/drivers/md/dm-bufio.c
===================================================================
--- linux-3.9-rc5-fast.orig/drivers/md/dm-bufio.c 2013-04-05 00:02:20.000000000 +0200
+++ linux-3.9-rc5-fast/drivers/md/dm-bufio.c 2013-04-05 00:59:15.000000000 +0200
@@ -319,6 +319,9 @@ static void __cache_size_refresh(void)
static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
enum data_mode *data_mode)
{
+ unsigned noio_flag;
+ void *ptr;
+
if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) {
*data_mode = DATA_MODE_SLAB;
return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask);
@@ -332,7 +335,26 @@ static void *alloc_buffer_data(struct dm
}
*data_mode = DATA_MODE_VMALLOC;
- return __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
+
+ /*
+ * __vmalloc allocates the data pages and auxiliary structures with
+ * gfp_flags that were specified, but pagetables are always allocated
+ * with GFP_KERNEL, no matter what was specified as gfp_mask.
+ *
+ * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that
+ * all allocations done by this process (including pagetables) are done
+ * as if GFP_NOIO was specified.
+ */
+
+ if (gfp_mask & __GFP_NORETRY)
+ noio_flag = memalloc_noio_save();
+
+ ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
+
+ if (gfp_mask & __GFP_NORETRY)
+ memalloc_noio_restore(noio_flag);
+
+ return ptr;
}
/*
--
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