[PATCH v2 2/2] dm crypt: do not wait for backlogged crypto request completion in softirq

Ignat Korchagin
2020-12-30T21:47:47Z

Commit 39d42fa96ba1b7d2544db3f8ed5da8fb0d5cb877 made it possible for some code
paths in dm-crypt to be executed in softirq context, when the underlying driver
processes IO requests in interrupt/softirq context.

When Crypto API backlogs a crypto request, dm-crypt uses wait_for_completion to
avoid sending further requests to an already overloaded crypto driver. However,
if the code is executing in softirq context, we might get the following
stacktrace:

[ 210.235213][ C0] BUG: scheduling while atomic: fio/2602/0x00000102
[ 210.236701][ C0] Modules linked in:
[ 210.237566][ C0] CPU: 0 PID: 2602 Comm: fio Tainted: G W 5.10.0+ #50
[ 210.239292][ C0] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
[ 210.241233][ C0] Call Trace:
[ 210.241946][ C0] <IRQ>
[ 210.242561][ C0] dump_stack+0x7d/0xa3
[ 210.243466][ C0] __schedule_bug.cold+0xb3/0xc2
[ 210.244539][ C0] __schedule+0x156f/0x20d0
[ 210.245518][ C0] ? io_schedule_timeout+0x140/0x140
[ 210.246660][ C0] schedule+0xd0/0x270
[ 210.247541][ C0] schedule_timeout+0x1fb/0x280
[ 210.248586][ C0] ? usleep_range+0x150/0x150
[ 210.249624][ C0] ? unpoison_range+0x3a/0x60
[ 210.250632][ C0] ? ____kasan_kmalloc.constprop.0+0x82/0xa0
[ 210.251949][ C0] ? unpoison_range+0x3a/0x60
[ 210.252958][ C0] ? __prepare_to_swait+0xa7/0x190
[ 210.254067][ C0] do_wait_for_common+0x2ab/0x370
[ 210.255158][ C0] ? usleep_range+0x150/0x150
[ 210.256192][ C0] ? bit_wait_io_timeout+0x160/0x160
[ 210.257358][ C0] ? blk_update_request+0x757/0x1150
[ 210.258582][ C0] ? _raw_spin_lock_irq+0x82/0xd0
[ 210.259674][ C0] ? _raw_read_unlock_irqrestore+0x30/0x30
[ 210.260917][ C0] wait_for_completion+0x4c/0x90
[ 210.261971][ C0] crypt_convert+0x19a6/0x4c00
[ 210.263033][ C0] ? _raw_spin_lock_irqsave+0x87/0xe0
[ 210.264193][ C0] ? kasan_set_track+0x1c/0x30
[ 210.265191][ C0] ? crypt_iv_tcw_ctr+0x4a0/0x4a0
[ 210.266283][ C0] ? kmem_cache_free+0x104/0x470
[ 210.267363][ C0] ? crypt_endio+0x91/0x180
[ 210.268327][ C0] kcryptd_crypt_read_convert+0x30e/0x420
[ 210.269565][ C0] blk_update_request+0x757/0x1150
[ 210.270563][ C0] blk_mq_end_request+0x4b/0x480
[ 210.271680][ C0] blk_done_softirq+0x21d/0x340
[ 210.272775][ C0] ? _raw_spin_lock+0x81/0xd0
[ 210.273847][ C0] ? blk_mq_stop_hw_queue+0x30/0x30
[ 210.275031][ C0] ? _raw_read_lock_irq+0x40/0x40
[ 210.276182][ C0] __do_softirq+0x190/0x611
[ 210.277203][ C0] ? handle_edge_irq+0x221/0xb60
[ 210.278340][ C0] asm_call_irq_on_stack+0x12/0x20
[ 210.279514][ C0] </IRQ>
[ 210.280164][ C0] do_softirq_own_stack+0x37/0x40
[ 210.281281][ C0] irq_exit_rcu+0x110/0x1b0
[ 210.282286][ C0] common_interrupt+0x74/0x120
[ 210.283376][ C0] asm_common_interrupt+0x1e/0x40
[ 210.284496][ C0] RIP: 0010:_aesni_enc1+0x65/0xb0

Fix this by making crypt_convert function reentrant from the point of a single
bio and make dm-crypt defer further bio processing to a workqueue, if Crypto API
backlogs a request in interrupt context.

Fixes: 39d42fa96ba1 ("dm crypt: add flags to optionally bypass kcryptd workq
ueues")
Cc: <stable@vger.kernel.org> # v5.9+

Signed-off-by: Ignat Korchagin <ignat@cloudflare.com>
---
drivers/md/dm-crypt.c | 102 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 97 insertions(+), 5 deletions(-)

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index e4fd690c70e1..0d939fbe51af 100644
--- a/drivers/md/dm-crypt.c
+++ b/drivers/md/dm-crypt.c
@@ -1539,13 +1539,19 @@ static void crypt_free_req(struct crypt_config *cc, void *req, struct bio *base_
* Encrypt / decrypt data from one bio to another one (can be the same one)
*/
static blk_status_t crypt_convert(struct crypt_config *cc,
- struct convert_context *ctx, bool atomic)
+ struct convert_context *ctx, bool atomic, bool reset_pending)
{
unsigned int tag_offset = 0;
unsigned int sector_step = cc->sector_size >> SECTOR_SHIFT;
int r;

- atomic_set(&ctx->cc_pending, 1);
+ /*
+ * if reset_pending is set we are dealing with the bio for the first time,
+ * else we're continuing to work on the previous bio, so don't mess with
+ * the cc_pending counter
+ */
+ if (reset_pending)
+ atomic_set(&ctx->cc_pending, 1);

while (ctx->iter_in.bi_size && ctx->iter_out.bi_size) {

@@ -1566,7 +1572,24 @@ static blk_status_t crypt_convert(struct crypt_config *cc,
* but the driver request queue is full, let's wait.
*/
case -EBUSY:
- wait_for_completion(&ctx->restart);
+ if (in_interrupt()) {
+ if (try_wait_for_completion(&ctx->restart)) {
+ /*
+ * we don't have to block to wait for completion,
+ * so proceed
+ */
+ } else {
+ /*
+ * we can't wait for completion without blocking
+ * exit and continue processing in a workqueue
+ */
+ ctx->r.req = NULL;
+ ctx->cc_sector += sector_step;
+ tag_offset++;
+ return BLK_STS_DEV_RESOURCE;
+ }
+ } else
+ wait_for_completion(&ctx->restart);
reinit_completion(&ctx->restart);
fallthrough;
/*
@@ -1958,6 +1981,37 @@ static bool kcryptd_crypt_write_inline(struct crypt_config *cc,
}
}

+static void kcryptd_crypt_write_continue(struct work_struct *work)
+{
+ struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
+ struct crypt_config *cc = io->cc;
+ struct convert_context *ctx = &io->ctx;
+ int crypt_finished;
+ sector_t sector = io->sector;
+ blk_status_t r;
+
+ wait_for_completion(&ctx->restart);
+ reinit_completion(&ctx->restart);
+
+ r = crypt_convert(cc, &io->ctx, true, false);
+ if (r)
+ io->error = r;
+ crypt_finished = atomic_dec_and_test(&ctx->cc_pending);
+ if (!crypt_finished && kcryptd_crypt_write_inline(cc, ctx)) {
+ /* Wait for completion signaled by kcryptd_async_done() */
+ wait_for_completion(&ctx->restart);
+ crypt_finished = 1;
+ }
+
+ /* Encryption was already finished, submit io now */
+ if (crypt_finished) {
+ kcryptd_crypt_write_io_submit(io, 0);
+ io->sector = sector;
+ }
+
+ crypt_dec_pending(io);
+}
+
static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)
{
struct crypt_config *cc = io->cc;
@@ -1986,7 +2040,17 @@ static void kcryptd_crypt_write_convert(struct dm_crypt_io *io)

crypt_inc_pending(io);
r = crypt_convert(cc, ctx,
- test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags));
+ test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags), true);
+ /*
+ * Crypto API backlogged the request, because its queue was full
+ * and we're in softirq context, so continue from a workqueue
+ * (TODO: is it actually possible to be in softirq in the write path?)
+ */
+ if (r == BLK_STS_DEV_RESOURCE) {
+ INIT_WORK(&io->work, kcryptd_crypt_write_continue);
+ queue_work(cc->crypt_queue, &io->work);
+ return;
+ }
if (r)
io->error = r;
crypt_finished = atomic_dec_and_test(&ctx->cc_pending);
@@ -2011,6 +2075,25 @@ static void kcryptd_crypt_read_done(struct dm_crypt_io *io)
crypt_dec_pending(io);
}

+static void kcryptd_crypt_read_continue(struct work_struct *work)
+{
+ struct dm_crypt_io *io = container_of(work, struct dm_crypt_io, work);
+ struct crypt_config *cc = io->cc;
+ blk_status_t r;
+
+ wait_for_completion(&io->ctx.restart);
+ reinit_completion(&io->ctx.restart);
+
+ r = crypt_convert(cc, &io->ctx, true, false);
+ if (r)
+ io->error = r;
+
+ if (atomic_dec_and_test(&io->ctx.cc_pending))
+ kcryptd_crypt_read_done(io);
+
+ crypt_dec_pending(io);
+}
+
static void kcryptd_crypt_read_convert(struct dm_crypt_io *io)
{
struct crypt_config *cc = io->cc;
@@ -2022,7 +2105,16 @@ static void kcryptd_crypt_read_convert(struct dm_crypt_io *io)
io->sector);

r = crypt_convert(cc, &io->ctx,
- test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags));
+ test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags), true);
+ /*
+ * Crypto API backlogged the request, because its queue was full
+ * and we're in softirq context, so continue from a workqueue
+ */
+ if (r == BLK_STS_DEV_RESOURCE) {
+ INIT_WORK(&io->work, kcryptd_crypt_read_continue);
+ queue_work(cc->crypt_queue, &io->work);
+ return;
+ }
if (r)
io->error = r;

--
2.20.1