3.2.46-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
commit 502624bdad3dba45dfaacaf36b7d83e39e74b2d2 upstream.
This patch uses memalloc_noio_save to avoid a possible deadlock in
dm-bufio. (it could happen only with large block size, at most
PAGE_SIZE << MAX_ORDER (typically 8MiB).
__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>
Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
[bwh: Backported to 3.2 as recommended]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
drivers/md/dm-bufio.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -322,6 +322,9 @@ 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);
@@ -335,7 +338,28 @@ 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 = current->flags & PF_MEMALLOC;
+ current->flags |= PF_MEMALLOC;
+ }
+
+ ptr = __vmalloc(c->block_size, gfp_mask, PAGE_KERNEL);
+
+ if (gfp_mask & __GFP_NORETRY)
+ current->flags = (current->flags & ~PF_MEMALLOC) | noio_flag;
+
+ return ptr;
}
/*
--
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