From: Abd-Alrhman Masalkhi Date: Thu, 11 Jun 2026 08:35:14 +0000 (+0000) Subject: md/raid1: honor REQ_NOWAIT when waiting for behind writes X-Git-Tag: v7.2-rc1~31^2~10^2~5 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a286cb88ddb26c5f4377859d8e77233d9181eb82;p=thirdparty%2Flinux.git md/raid1: honor REQ_NOWAIT when waiting for behind writes raid1 supports REQ_NOWAIT reads by avoiding waits in the barrier path through wait_read_barrier(). However, a read can still block on a WriteMostly device when the array uses a bitmap and there are outstanding behind writes. In that case raid1 unconditionally calls wait_behind_writes(), which may sleep until all behind writes complete. As a result, a REQ_NOWAIT read can block despite the caller explicitly requesting non-blocking behavior. This ensures that raid1 consistently honors REQ_NOWAIT reads across all paths that may otherwise wait for behind writes. Fixes: 5aa705039c4f ("md: raid1 add nowait support") Signed-off-by: Abd-Alrhman Masalkhi Link: https://patch.msgid.link/20260611083514.754922-1-abd.masalkhi@gmail.com Signed-off-by: Yu Kuai --- diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c index 7d778fe1c47ca..0f02e2956398d 100644 --- a/drivers/md/md-bitmap.c +++ b/drivers/md/md-bitmap.c @@ -2064,18 +2064,23 @@ static void bitmap_end_behind_write(struct mddev *mddev) bitmap->mddev->bitmap_info.max_write_behind); } -static void bitmap_wait_behind_writes(struct mddev *mddev) +static bool bitmap_wait_behind_writes(struct mddev *mddev, bool nowait) { struct bitmap *bitmap = mddev->bitmap; /* wait for behind writes to complete */ if (bitmap && atomic_read(&bitmap->behind_writes) > 0) { + if (nowait) + return false; + pr_debug("md:%s: behind writes in progress - waiting to stop.\n", mdname(mddev)); /* need to kick something here to make sure I/O goes? */ wait_event(bitmap->behind_wait, atomic_read(&bitmap->behind_writes) == 0); } + + return true; } static void bitmap_destroy(struct mddev *mddev) @@ -2085,7 +2090,7 @@ static void bitmap_destroy(struct mddev *mddev) if (!bitmap) /* there was no bitmap */ return; - bitmap_wait_behind_writes(mddev); + bitmap_wait_behind_writes(mddev, false); if (!test_bit(MD_SERIALIZE_POLICY, &mddev->flags)) mddev_destroy_serial_pool(mddev, NULL); diff --git a/drivers/md/md-bitmap.h b/drivers/md/md-bitmap.h index 214f623c7e790..f46674bdfeb91 100644 --- a/drivers/md/md-bitmap.h +++ b/drivers/md/md-bitmap.h @@ -98,7 +98,7 @@ struct bitmap_operations { void (*start_behind_write)(struct mddev *mddev); void (*end_behind_write)(struct mddev *mddev); - void (*wait_behind_writes)(struct mddev *mddev); + bool (*wait_behind_writes)(struct mddev *mddev, bool nowait); md_bitmap_fn *start_write; md_bitmap_fn *end_write; diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c index 1adc5b1178216..5a4e2abaa7577 100644 --- a/drivers/md/md-llbitmap.c +++ b/drivers/md/md-llbitmap.c @@ -1574,16 +1574,19 @@ static void llbitmap_end_behind_write(struct mddev *mddev) wake_up(&llbitmap->behind_wait); } -static void llbitmap_wait_behind_writes(struct mddev *mddev) +static bool llbitmap_wait_behind_writes(struct mddev *mddev, bool nowait) { struct llbitmap *llbitmap = mddev->bitmap; - if (!llbitmap) - return; + if (llbitmap && atomic_read(&llbitmap->behind_writes) > 0) { + if (nowait) + return false; - wait_event(llbitmap->behind_wait, - atomic_read(&llbitmap->behind_writes) == 0); + wait_event(llbitmap->behind_wait, + atomic_read(&llbitmap->behind_writes) == 0); + } + return true; } static ssize_t bits_show(struct mddev *mddev, char *page) diff --git a/drivers/md/md.c b/drivers/md/md.c index 096bb64e87bd5..d1465bcd86c81 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -7050,7 +7050,7 @@ EXPORT_SYMBOL_GPL(md_stop_writes); static void mddev_detach(struct mddev *mddev) { if (md_bitmap_enabled(mddev, false)) - mddev->bitmap_ops->wait_behind_writes(mddev); + mddev->bitmap_ops->wait_behind_writes(mddev, false); if (mddev->pers && mddev->pers->quiesce && !is_md_suspended(mddev)) { mddev->pers->quiesce(mddev, 1); mddev->pers->quiesce(mddev, 0); diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c index 86d4f224ffb11..e2a50816e5a06 100644 --- a/drivers/md/raid1.c +++ b/drivers/md/raid1.c @@ -1341,6 +1341,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio, int max_sectors; int rdisk; bool r1bio_existed = !!r1_bio; + bool nowait = bio->bi_opf & REQ_NOWAIT; /* * An md cloned bio indicates we are in the error path. @@ -1360,8 +1361,7 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio, * Still need barrier for READ in case that whole * array is frozen. */ - if (!wait_read_barrier(conf, bio->bi_iter.bi_sector, - bio->bi_opf & REQ_NOWAIT)) { + if (!wait_read_barrier(conf, bio->bi_iter.bi_sector, nowait)) { bio_wouldblock_error(bio); return; } @@ -1402,7 +1402,11 @@ static void raid1_read_request(struct mddev *mddev, struct bio *bio, * over-take any writes that are 'behind' */ mddev_add_trace_msg(mddev, "raid1 wait behind writes"); - mddev->bitmap_ops->wait_behind_writes(mddev); + if (!mddev->bitmap_ops->wait_behind_writes(mddev, nowait)) { + bio_wouldblock_error(bio); + set_bit(R1BIO_Returned, &r1_bio->state); + goto err_handle; + } } if (max_sectors < bio_sectors(bio)) {