Commit 502624bd authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Alasdair G Kergon

dm bufio: avoid a possible __vmalloc deadlock

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: default avatarMikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 09e8b813
...@@ -319,6 +319,9 @@ static void __cache_size_refresh(void) ...@@ -319,6 +319,9 @@ static void __cache_size_refresh(void)
static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
enum data_mode *data_mode) enum data_mode *data_mode)
{ {
unsigned noio_flag;
void *ptr;
if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) { if (c->block_size <= DM_BUFIO_BLOCK_SIZE_SLAB_LIMIT) {
*data_mode = DATA_MODE_SLAB; *data_mode = DATA_MODE_SLAB;
return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask); return kmem_cache_alloc(DM_BUFIO_CACHE(c), gfp_mask);
...@@ -332,7 +335,26 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask, ...@@ -332,7 +335,26 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
} }
*data_mode = DATA_MODE_VMALLOC; *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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