On Mon, Mar 06 2023 at 9:12P -0500, Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: > Hi, > > On 3/7/2023 3:31 AM, Mike Snitzer wrote: > > On Mon, Mar 06 2023 at 8:49P -0500, > > Hou Tao <houtao@xxxxxxxxxxxxxxx> wrote: > > > >> From: Hou Tao <houtao1@xxxxxxxxxx> > >> > >> When neither no_read_workqueue nor no_write_workqueue are enabled, > >> tasklet_trylock() in crypt_dec_pending() may still return false due to > >> an uninitialized state, and dm-crypt will do io completion in io_queue > >> instead of current context unnecessarily. > > Have you actually experienced this? > > Yes. I had written a bpftrace script to check the completion context of > blkdev_bio_end_io_simple() when doing direct io read on dm-crypt device. The > expected context should be unbound workers of crypt_queue, but sometimes the > context is the bound worker of io_queue. OK, thanks for clarifying. Curious to know the circumstance (I thought per-bio-data is zero'd -- but it may be I'm mistaken). I won't be marking this commit for stable@ but if others feel differently please let me know and I'll do so. (We can always propose it to stable@, after the fact, even if the commit header doesn't Cc stable@) > >> Fix it by initializing io->tasklet in crypt_io_init(). > > Really would rather avoid always calling tasklet_init(). But I can > > optimize it away with a later patch. > > My first though was "io->tasklet.state = 0", but it may be fragile because it > operated on the internal status of tasklet, so I switch to tasklet_init(). Yes, I looked into it and came up with the same hack.. and I too felt it was too fragile due to open-coding direct access to the tasklet's members. I have a patch I just staged that staged that uses jump_labels to optimize this code. If you might review/test/verify it works well for you that'd be appreciated: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=ae75a25bd83f7c541240449d2fff3a44433e506b It builds on your patch, which I added a comment to: https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=d9fe0a98a2e0a1cf585e8a6555afb33be968bd13 From: Mike Snitzer <snitzer@xxxxxxxxxx> Date: Mon, 6 Mar 2023 15:58:33 -0500 Subject: [PATCH] dm crypt: conditionally enable code needed for tasklet usecases Use jump_label to limit the need for branching, and tasklet_init(), unless either of the optional "no_read_workqueue" and/or "no_write_workqueue" features are used. Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx> --- drivers/md/dm-crypt.c | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c index 641457e72603..2d0309ca07f5 100644 --- a/drivers/md/dm-crypt.c +++ b/drivers/md/dm-crypt.c @@ -40,6 +40,7 @@ #include <keys/user-type.h> #include <keys/encrypted-type.h> #include <keys/trusted-type.h> +#include <linux/jump_label.h> #include <linux/device-mapper.h> @@ -85,6 +86,8 @@ struct dm_crypt_io { struct rb_node rb_node; } CRYPTO_MINALIGN_ATTR; +static DEFINE_STATIC_KEY_FALSE(use_tasklet_enabled); + struct dm_crypt_request { struct convert_context *ctx; struct scatterlist sg_in[4]; @@ -1730,12 +1733,15 @@ static void crypt_io_init(struct dm_crypt_io *io, struct crypt_config *cc, io->sector = sector; io->error = 0; io->ctx.r.req = NULL; - /* - * tasklet_init() here to ensure crypt_dec_pending()'s - * tasklet_trylock() doesn't incorrectly return false - * even when tasklet isn't in use. - */ - tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, (unsigned long)&io->work); + if (static_branch_unlikely(&use_tasklet_enabled)) { + /* + * tasklet_init() here to ensure crypt_dec_pending()'s + * tasklet_trylock() doesn't incorrectly return false + * even when tasklet isn't in use. + */ + tasklet_init(&io->tasklet, kcryptd_crypt_tasklet, + (unsigned long)&io->work); + } io->integrity_metadata = NULL; io->integrity_metadata_from_pool = false; atomic_set(&io->io_pending, 0); @@ -1775,6 +1781,10 @@ static void crypt_dec_pending(struct dm_crypt_io *io) kfree(io->integrity_metadata); base_bio->bi_status = error; + if (!static_branch_unlikely(&use_tasklet_enabled)) { + bio_endio(base_bio); + return; + } /* * If we are running this function from our tasklet, @@ -2232,8 +2242,9 @@ static void kcryptd_queue_crypt(struct dm_crypt_io *io) { struct crypt_config *cc = io->cc; - if ((bio_data_dir(io->base_bio) == READ && test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags)) || - (bio_data_dir(io->base_bio) == WRITE && test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags))) { + if (static_branch_unlikely(&use_tasklet_enabled) && + ((bio_data_dir(io->base_bio) == READ && test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags)) || + (bio_data_dir(io->base_bio) == WRITE && test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags)))) { /* * in_hardirq(): Crypto API's skcipher_walk_first() refuses to work in hard IRQ context. * irqs_disabled(): the kernel may run some IO completion from the idle thread, but @@ -2746,6 +2757,10 @@ static void crypt_dtr(struct dm_target *ti) crypt_calculate_pages_per_client(); spin_unlock(&dm_crypt_clients_lock); + if (test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags) || + test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags)) + static_branch_dec(&use_tasklet_enabled); + dm_audit_log_dtr(DM_MSG_PREFIX, ti, 1); } @@ -3375,6 +3390,10 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv) ti->limit_swap_bios = true; ti->accounts_remapped_io = true; + if (test_bit(DM_CRYPT_NO_READ_WORKQUEUE, &cc->flags) || + test_bit(DM_CRYPT_NO_WRITE_WORKQUEUE, &cc->flags)) + static_branch_inc(&use_tasklet_enabled); + dm_audit_log_ctr(DM_MSG_PREFIX, ti, 1); return 0; -- 2.37.1 (Apple Git-137.1) -- dm-devel mailing list dm-devel@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/dm-devel
