Commit b330e6a49dc3 ("md: convert to kvmalloc") uses kvmalloc_array()
to allocate memory with GFP_NOIO flag in resize_chunks() via function
scribble_alloc(),
2269 err = scribble_alloc(percpu, new_disks,
2270 new_sectors / STRIPE_SECTORS,
2271 GFP_NOIO);
The purpose of GFP_NOIO flag to kvmalloc_array() is to allocate
non-physically continuous pages and avoid extra I/Os of page reclaim
which triggered by memory allocation. When system memory is under
heavy pressure, non-physically continuous pages allocation is more
probably to success than allocating physically continuous pages.
But as a non GFP_KERNEL compatible flag, GFP_NOIO is not acceptible
by kvmalloc_node() and the memory allocation indeed is handled with
kmalloc_node() to allocate physically continuous pages. This is not
the expected behavior of the original purpose when mistakenly using
GFP_NOIO flag.
In this patch, the memalloc scope APIs memalloc_noio_save() and
memalloc_noio_restore() are used when calling scribble_alloc(). Then
when calling kvmalloc_array() with GFP_KERNEL mask, the scope APIs
may indicatet the allocating context to avoid memory reclaim related
I/Os, to avoid recursive I/O deadlock on the md raid array itself
which is calling scribble_alloc() to allocate non-physically continuous
pages.
This patch also removes gfp_t flags from scribble_alloc() parameters
list, because the invalid GFP_NOIO is replaced by memalloc scope APIs.
Fixes: b330e6a49dc3 ("md: convert to kvmalloc")
Signed-off-by: Coly Li <colyli@xxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
---
drivers/md/raid5.c | 22 ++++++++++++++++------
1 file changed, 16 insertions(+), 6 deletions(-)
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index ba00e9877f02..6b23f8aba169 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2228,14 +2228,15 @@ static int grow_stripes(struct r5conf *conf, int num)
* of the P and Q blocks.
*/
static int scribble_alloc(struct raid5_percpu *percpu,
- int num, int cnt, gfp_t flags)
+ int num, int cnt)
{
size_t obj_size =
sizeof(struct page *) * (num+2) +
sizeof(addr_conv_t) * (num+2);
void *scribble;
+ unsigned int noio_flag;
- scribble = kvmalloc_array(cnt, obj_size, flags);
+ scribble = kvmalloc_array(cnt, obj_size, GFP_KERNEL);
if (!scribble)
return -ENOMEM;
@@ -2250,6 +2251,7 @@ static int resize_chunks(struct r5conf *conf, int new_disks, int new_sectors)
{
unsigned long cpu;
int err = 0;
+ unsigned int noio_flag;
/*
* Never shrink. And mddev_suspend() could deadlock if this is called
@@ -2262,16 +2264,25 @@ static int resize_chunks(struct r5conf *conf, int new_disks, int new_sectors)
mddev_suspend(conf->mddev);
get_online_cpus();
+ /*
+ * scribble_alloc() allocates memory by kvmalloc_array(), if
+ * the memory allocation triggers memory reclaim I/Os onto
+ * this raid array, there might be potential deadlock if this
+ * raid array happens to be suspended during memory allocation.
+ * Here the scope APIs are used to disable such recursive memory
+ * reclaim I/Os.
+ */
+ noio_flag = memalloc_noio_save();
for_each_present_cpu(cpu) {
struct raid5_percpu *percpu;
percpu = per_cpu_ptr(conf->percpu, cpu);
err = scribble_alloc(percpu, new_disks,
- new_sectors / STRIPE_SECTORS,
- GFP_NOIO);
+ new_sectors / STRIPE_SECTORS);
if (err)
break;
}
+ memalloc_noio_restore(noio_flag);
put_online_cpus();
mddev_resume(conf->mddev);
@@ -6759,8 +6770,7 @@ static int alloc_scratch_buffer(struct r5conf *conf, struct raid5_percpu *percpu
conf->previous_raid_disks),
max(conf->chunk_sectors,
conf->prev_chunk_sectors)
- / STRIPE_SECTORS,
- GFP_KERNEL)) {
+ / STRIPE_SECTORS)) {
free_scratch_buffer(conf, percpu);
return -ENOMEM;
}
--
2.25.0
