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;