diff options
author | Mikulas Patocka <mpatocka@redhat.com> | 2013-05-10 14:37:15 +0100 |
---|---|---|
committer | Alasdair G Kergon <agk@redhat.com> | 2013-05-10 14:37:15 +0100 |
commit | 502624bdad3dba45dfaacaf36b7d83e39e74b2d2 (patch) | |
tree | 56c7d8236425193eb21730f2591868c735db9a5a | |
parent | 09e8b813897a0f85bb401435d009228644c81214 (diff) |
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: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
-rw-r--r-- | drivers/md/dm-bufio.c | 24 |
1 files changed, 23 insertions, 1 deletions
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c index c6083132c4b8..0387e05cdb98 100644 --- a/drivers/md/dm-bufio.c +++ b/drivers/md/dm-bufio.c @@ -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_bufio_client *c, gfp_t gfp_mask, } *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; } /* |