Add the driver internals to build WRITE_FULL_TRACK FCX channel programs
in response to unformatted tracks on ESE devices.
struct dasd_ccw_req: filldata, a pointer to the per-track metadata (an R0
record and the count records) that the WRITE_FULL_TRACK TIDAWs point at,
and format/start_trk/end_trk/collision that link a request to its
format-track guard entry so an overlapping format request can be detected.
struct dasd_device: fill_mem/fill_chunks pool for those buffers and a
zeroed nulldata page used as the data source for pad records.
struct dasd_block: ese_staging/ese_lock, a hardirq-safe staging list. An
ESE format CQR is created in the interrupt handler but has to be enqueued
on ccw_queue under queue_lock; taking queue_lock while the ccwdev_lock is
held there would invert the lock order, so the CQR is staged under ese_lock
and dasd_block_tasklet splices it onto ccw_queue. Existing locking is
unchanged.
Add CQR states DASD_CQR_ABORT/ABORTED to retire the origin CQR of a
replaced write without completing it to the block layer, and struct
eckd_r0 for the track header record.
The CCW and ESE format pools are enlarged (a full-track ITCW is roughly
twice a plain track-mode one) to keep two maximum-size requests in flight.
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-9-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The track address of an Extended Address Volume (more than 65520
cylinders) carries the high cylinder bits that do not fit the 16-bit cyl
field in the upper part of the head field. set_ch_t() open-codes the
corresponding shifts; name them so the encoding is explicit and can be
reused.
No functional change.
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-8-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
dasd_alloc_device() runs in process context (device set_online), so its
pool allocations do not need GFP_ATOMIC. Use GFP_KERNEL instead, which is
more reliable, especially for the larger DMA allocations that later ESE
full-track work adds here.
No functional change intended.
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-7-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With 4096-byte blocks a full ECKD track holds exactly 12 records. Lower
DASD_ECKD_MAX_BLOCKS from 190 to 180 so requests align to track
boundaries (15 full tracks); full-track I/O is more efficient than
partial-track writes, and 190 had no alignment significance and could
let a request cross a track boundary.
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-6-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
__dasd_cleanup_cqr() maps the completion result to a block status by
reading cqr->intrc, but only after discipline->free_cp() has returned the
request block to its memory pool (dasd_eckd_free_cp() ends in
dasd_sfree_request()). On SMP another CPU can reallocate that block and
overwrite cqr->intrc before it is read, completing the request with the
wrong error. proc_bytes is already snapshotted before free_cp() for the
same reason; do the same for intrc.
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-5-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Several sysfs show/store handlers call a discipline callback that
dereferences device->private, either directly or through the
DASD_DEFINE_ATTR() macro. During dasd_generic_set_online() the discipline
is assigned before check_device() allocates device->private, so an
unprivileged read of one of these world-readable attributes in that window
dereferences a NULL pointer and panics.
Guard the dereference inside each callback that actually touches
device->private.
Fixes: c729696bcf ("s390/dasd: Recognise data for ESE volumes")
Cc: stable@vger.kernel.org
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-4-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
dasd_default_erp_postaction() copies the timing and device state from
the finished ERP request back to the original request but drops
proc_bytes. A request that was partially completed, an ESE read of a
not-yet-allocated track returns fewer bytes than requested, and then
recovered through the ERP chain loses its partial-completion length.
__dasd_cleanup_cqr() then sees proc_bytes == 0 and completes the whole
request instead of requeueing the remainder, silently returning zeroed
data for the part that was never read.
Carry proc_bytes over to the original request like the other
per-request state.
Fixes: 5e6bdd37c5 ("s390/dasd: fix data corruption for thin provisioned devices")
Cc: stable@vger.kernel.org
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-3-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
dasd_int_handler() completes an NRF read of an unallocated ESE track by
calling ese_read() and unconditionally marking the request
DASD_CQR_SUCCESS. dasd_eckd_ese_read() can return an error before it has
zeroed the destination buffer: a failed sense-data parse or a current
track outside the requested range both return early, leaving the
destination pages untouched. The request is still completed successfully,
so the block layer is handed stale / uninitialized memory instead of
zeros.
Check the ese_read() return value and fail the request through the normal
error path instead of forcing DASD_CQR_SUCCESS.
Fixes: 5e6bdd37c5 ("s390/dasd: fix data corruption for thin provisioned devices")
Cc: stable@vger.kernel.org
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Stefan Haberland <sth@linux.ibm.com>
Link: https://patch.msgid.link/20260805111612.1285190-2-sth@linux.ibm.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ioc_pd_stat() reads ioc->enabled, ioc->vtime_base_rate, and
iocg->last_stat without holding ioc->lock, which trips KCSAN since
ioc_adjust_base_vrate() and iocg_flush_stat_upward() write those
fields under ioc->lock.
Commit 35198e3230 fixed the same issue in ioc_qos_prfill() and
ioc_cost_model_prfill() by adding spin_lock_irq(&ioc->lock). However,
those functions read configuration parameters (qos/model) that need
synchronized reads. In contrast, ioc_pd_stat() only reads stat
values (vrate, usage) where stale reads are harmless, so data_race()
is more appropriate — it silences the KCSAN warning without adding
lock contention during high-frequency stat reads.
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://patch.msgid.link/20260804054120.161933-1-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Check the BIP_CHECK flags before generating or verifying PI information,
otherwise this can be incorrectly called for non-PI metadata and
cause generation of incorrect metadata and crashed in the verification
handler.
The new behavior matches that of the block layer auto-generated
metadata.
Fixes: 0bde8a12b5 ("block: add fs_bio_integrity helpers")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Anuj Gupta <anuj20.g@samsung.com>
Link: https://patch.msgid.link/20260804123928.736596-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
zloop divides the requested capacity by the zone size to determine the
number of zones. Since it uses one zone size for all zones, a smaller last
zone is not supported and an unaligned capacity is rounded down.
The capacity_mb description incorrectly states that the capacity is rounded
up. Correct it to document the actual behavior.
Fixes: 9e4f11c122 ("Documentation: Document the new zoned loop block device driver")
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/4659F8F0C6C328EA+20260804052942.1186727-1-raoxu@uniontech.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ublk_batch_commit_io() stored the new auto_buf into io->buf before
calling ublk_clear_auto_buf_reg(). Clear takes the unregister index
from io->buf.auto_reg, so it could drop the new slot and leave the
old registered buffer behind.
Fixes: 1e500e106d ("ublk: handle UBLK_U_IO_COMMIT_IO_CMDS")
Signed-off-by: Yang Xiuwei <yangxiuwei@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blkdev.h gets included in various places outside the block layer just
for struct blk_plug and related plugging functions.
Split blk_plug into a separate helper to reduce the amount of code
that needs to get rebuilt when blkdev.h changes and to slightly
reduce compile times.
In io_uring this requires pulling in a few other headers explicitly that
previously were implicitly included through blkdev.h.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Christian Brauner (Amutable) <brauner@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://patch.msgid.link/20260804125524.740996-1-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blk_zone_wplug_handle_zone_mgmt now only checks that zone reset and
zone finish operations are directed to a sequential write required
zone. This has nothing to do with zone write plugs and is better
handled with other bio validity checks in submit_bio_noacct.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://patch.msgid.link/20260804125038.740388-4-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Commit efae226c2e ("block: handle zone management operations
completions") moved all block layer tracking of zone management
operations to the I/O completion handler. With that REQ_NOWAIT zone
management operations are just fine, so allow them.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://patch.msgid.link/20260804125038.740388-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The size of a sequential zone backing file records the amount of data
written and is used to restore the zone state. A backing file whose size
is equal to the zone capacity is restored as a full zone, while a file
larger than the zone capacity is rejected as invalid.
However, zloop_finish_zone() currently truncates the backing file to the
zone size. For devices with a reduced zone capacity, finishing a zone
therefore creates a backing file larger than the zone capacity. After the
device is removed and later re-added, that zone file is rejected instead
of being restored as a full zone.
Truncate finished sequential zones to the zone capacity, matching the
persistent representation accepted by zloop_update_seq_zone() for a full
zone.
Suggested-by: Damien Le Moal <dlemoal@kernel.org>
Fixes: eb0570c7df ("block: new zoned loop block device driver")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Link: https://patch.msgid.link/B39E5FD81D1A07F4+20260804023403.939767-1-raoxu@uniontech.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Batch AUTO_BUF_REG COMMIT must unregister the old auto_buf index before
storing the next one. Fixed per-tag indexing (A == B) masks bugs that
clear after overwriting io->buf.
Add kublk --rotate_auto_buf so each tag alternates between two sparse
buffer indices, and test_batch_04.sh to exercise that path. Without the
driver fix, the request ref stays stuck and I/O hangs; the test uses a
short timeout and kills the ublk daemon to recover. With the fix, a
small write completes quickly.
Signed-off-by: Yang Xiuwei <yangxiuwei@kylinos.cn>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260730024050.1062354-1-yangxiuwei@kylinos.cn
Signed-off-by: Jens Axboe <axboe@kernel.dk>
With UBLK_F_AUTO_BUF_REG, invalid sqe->addr can fail after
ublk_fill_io_cmd() has set UBLK_IO_FLAG_ACTIVE. The uring_cmd is
completed while the tag stays active, which can hang teardown.
Split validation from buffer apply so the check has no side effects,
then take the uring_cmd and store the already-validated buffer. Apply
the same order in FETCH so io->buf is not written before __ublk_fetch()
state checks.
Fixes: 52460dda3a ("ublk: move auto buffer register handling into one dedicated helper")
Suggested-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Yang Xiuwei <yangxiuwei@kylinos.cn>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ublk_map_io() and ublk_unmap_io() are no-ops for ublk devices that
enable user copy or zero copy, as well as for requests without data to
copy in the given direction. However, the implementation is a bit
convoluted, returning the full request data length and relying on the
caller to check the return value against the request length.
UBLK_F_SHMEM_ZC recently added branches to skip the ublk_{,un}map_io()
call for I/Os using a shared-memory buffer. This is a more logical place
for the device need_map and the ublk_need_{,un}map_req() checks, so move
them there from ublk_{,un}map_io().
Checking these conditions early also skips the expensive pointer-chasing
for the ublk_iod_is_shmem_zc() check in __ublk_complete_rq() for the
common case of a ublk device using user copy or zero copy.
Drop the req_op() filter in __ublk_complete_rq(), as it's redundant with
the ublk_need_unmap_req() check.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260803211441.2538144-9-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Add an optional --io_desc_size argument to the kublk add/recover
commands to enable UBLK_F_IO_DESC on the ublk device. The mmap()
arguments and ublk_get_iod() computation are adjusted accordingly.
Display the configured io_desc_size in the kublk list output for ublk
devices with UBLK_F_IO_DESC.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260803211441.2538144-7-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ublk passes the parameters of incoming I/O in memory shared between the
kernel ublk driver and userspace ublk server in struct ublksrv_io_desc.
The size of this struct is currently fixed to 24 bytes, which has been
an obstacle to extending it with additional fields [1]. Additionally,
with multiple ublk server threads handling I/Os from the same ublk queue
(possible with UBLK_F_PER_IO_DAEMON or UBLK_F_BATCH_IO), false sharing
results from adjacent io_descs sharing the same cache line.
Add a ublk feature UBLK_F_IO_DESC_SIZE to allow a ublk server to
override the size of each io_desc. The size must be at least 24 and a
multiple of 8 to store a properly-aligned struct ublksrv_io_desc. It's
also limited to a maximum of 256, though this bound could be lifted in
the future.
The struct ublksrv_io_desc is located at the beginning of each io_desc
and the remainder is padding. The mmap() performed for each queue must
have a length of queue_depth * io_desc_size rounded up to the page size.
The mmap() offset must be q_id * UBLK_MAX_QUEUE_DEPTH * io_desc_size,
also rounded up to the page size.
[1]: https://lore.kernel.org/linux-block/aV8QfvaNO5P6vOs6@fedora/
Suggested-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260803211441.2538144-6-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ublk_setup_iod() is currently called to populate struct ublksrv_io_desc
on the thread submitting I/O to a ublk device. However, only the ublk
server threads read the io_descs. This basically guarantees a cache miss
on both threads for each ublk I/O. There's really no need to initialize
the io_descs on the submitting thread. Move the ublk_setup_iod() call to
ublk_dispatch_req() (for non-UBLK_F_BATCH_IO) and
__ublk_batch_prep_dispatch() (for UBLK_F_BATCH_IO), which runs on the
ublk server daemon thread before dispatching the I/O to userspace.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260803211441.2538144-5-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
In preparation for moving the struct ublksrv_io_desc initialization from
the thread submitting ublk requests to the daemon thread receiving them,
split the fallible part of ublk_setup_iod{,_zoned}() into new helper
ublk_validate_req{,_zoned}(). Only ublk_setup_iod{,_zoned}() accesses
the io_desc and cannot error out.
Return a bool value from ublk_validate_req{,_zoned}() as the existing
error code ublk_setup_iod{,_zoned}() returns is only checked against
BLK_STS_OK.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260803211441.2538144-4-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The u16 nr_hw_queues and queue_depth fields of the ublk UAPI struct
ublksrv_ctrl_dev_info constrain the number of queues and queue depth of
each ublk device. However, the ublk driver is a bit inconsistent with
the type it uses to represent these values, mixing u16 with int and
unsigned int. Change all queue number, queue depth, q_id, and tag
variables/fields to u16 to save some space.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Link: https://patch.msgid.link/20260803211441.2538144-2-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
io->res is set from struct ublksrv_io_cmd's result field, which is
controlled by the ublk server process, without any validation. It's thus
possible for userspace to trigger the io->res > rq_bytes warning.
ublk_copy_user_pages() already limits the copy length to the request
data length, so drop the warning.
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260729171041.45061-4-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
If the userspace ublk server passes an unmapped address as the data
buffer for a completed ublk read, ublk_unmap_io() will return 0
indicating no bytes could be copied. Currently, this will result in
calling blk_update_request() with nr_bytes=0, which doesn't seem
supported. Fail the I/O with BLK_STS_IOERR in this case instead.
Fixes: 71f28f3136 ("ublk_drv: add io_uring based userspace block driver")
Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://patch.msgid.link/20260729171041.45061-3-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
The last_check_time field in throtl_grp was used by the
CONFIG_BLK_DEV_THROTTLING_LOW mechanism (in throtl_upgrade_check() and
the downgrade logic) to timestamp the last upgrade/downgrade check.
Commit bf20ab538c ("blk-throttle: remove CONFIG_BLK_DEV_THROTTLING_LOW")
removed all five of its uses in blk-throttle.c and the surrounding LOW
fields (latency_target, last_finish_time, checked_last_finish_time,
avg_idletime, idletime_threshold, bio_cnt, bad_bio_cnt,
bio_cnt_reset_time), but missed the field definition itself.
It has been a dead field since then: zero references in blk-throttle.c
and the whole tree. Remove it.
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Reviewed-by: Tang Yizhou <yizhou.tang@shopee.com>
Link: https://patch.msgid.link/20260717054855.2018578-1-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
kyber_timer_fn() sums the per-cpu latency histograms with
for_each_online_cpu(). A CPU that goes offline mid-interval leaves its
bucket un-flushed; the samples are lost from the current decision and
re-appear (stale) when the CPU is onlined again.
Fixes: 6e25cb01ea ("kyber: implement improved heuristics")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-5-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
ioc_lat_stat() walks ioc->pcpu_stat with for_each_online_cpu() to
compute missed-ppm and rq_wait deltas. An offlined CPU is skipped, so
its delta is dropped from the period and its last_* watermark is not
advanced; on re-online the next collection sees a delta spanning the
whole offline interval, corrupting the latency/vrate picture.
Fixes: 7caa47151a ("blkcg: implement blk-iocost")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-4-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
iolatency_check_latencies() and iolatency_ssd_stat() iterate a blkg's
per-cpu latency stats with for_each_online_cpu(). When a CPU that has
accumulated io.latency samples goes offline, its bucket is skipped: the
check loop (which also resets) neither sums nor clears it, and the show
path under-reports. On re-online the stranded samples are flushed into
a later check window, which can trigger a spurious throttle/scale
adjustment.
Fixes: d706751215 ("block: introduce blk-iolatency io controller")
Fixes: 1fa2840e56 ("blk-iolatency: use a percentile approache for ssd's")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-3-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blk_stat_timer_fn() sums and resets a callback's per-cpu buckets using
for_each_online_cpu(). A CPU that goes offline with pending samples is
skipped, so its samples are neither accumulated into the window nor
cleared; they sit in the bucket until the CPU comes back online, at
which point the stale values are flushed into whatever window is then
running.
This silently corrupts the latency picture that consumers (notably
writeback throttling via wbt, and blk-mq latency tracking) base
decisions on around CPU hotplug: under-counting while the CPU is
offline, then a burst of stale data on re-online.
Fixes: 34dbad5d26 ("blk-stat: convert to callback-based statistics reporting")
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260720093726.28965-2-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When switching IO schedulers on a block device, blkcg_activate_policy()
can race with concurrent blkcg deletion, leading to a use-after-free in
rcu_accelerate_cbs.
T1: T2:
blkg_destroy
kill(&blkg->refcnt) // blkg->refcnt=1->0
blkg_release // call_rcu(__blkg_release)
...
blkg_free_workfn
->pd_free_fn(pd)
elv_iosched_store
elevator_switch
...
iterate blkg list
blkg_get(blkg) // blkg->refcnt=0->1
list_del_init(&blkg->q_node)
blkg_put(pinned_blkg) // blkg->refcnt=1->0
blkg_release // call_rcu again
rcu_accelerate_cbs // uaf
Fix this by checking hlist_unhashed(&blkg->blkcg_node) before getting
a reference to the blkg. This is the same check used in blkg_destroy()
to detect if a blkg has already been destroyed. If the blkg is already
unhashed, skip processing it since it's being destroyed.
Fixes: f1c006f1c6 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()")
Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
Reviewed-by: Tang Yizhou <yizhou.tang@shopee.com>
Signed-off-by: Yu Kuai <yukuai@fygo.io>
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://patch.msgid.link/20260802112525.3933753-4-yukuai@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
When switching an IO scheduler on a block device, blkcg_activate_policy()
allocates blkg_policy_data (pd) for all blkgs attached to the queue.
However, blkcg_activate_policy() may race with concurrent blkcg deletion,
leading to use-after-free and memory leak issues.
The use-after-free occurs in the following race:
T1 (blkcg_activate_policy):
- Successfully allocates pd for blkg1 (loop0->queue, blkcgA)
- Fails to allocate pd for blkg2 (loop0->queue, blkcgB)
- Enters the enomem rollback path to release blkg1 resources
T2 (blkcg deletion):
- blkcgA is deleted concurrently
- blkg1 is freed via blkg_free_workfn()
- blkg1->pd is freed
T1 (continued):
- Rollback path accesses blkg1->pd->online after pd is freed
- Triggers use-after-free
In addition, blkg_free_workfn() frees pd before removing the blkg from
q->blkg_list. This allows blkcg_activate_policy() to allocate a new pd
for a blkg that is being destroyed, leaving the newly allocated pd
unreachable when the blkg is finally freed.
Fix these races by extending blkcg_mutex coverage to serialize
blkcg_activate_policy() rollback and blkg destruction, ensuring pd
lifecycle is synchronized with blkg list visibility.
Fixes: f1c006f1c6 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()")
Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
Reviewed-by: Tang Yizhou <yizhou.tang@shopee.com>
Signed-off-by: Yu Kuai <yukuai@fygo.io>
Reviewed-by: Tao Cui <cuitao@kylinos.cn>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Link: https://patch.msgid.link/20260802112525.3933753-3-yukuai@kernel.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
blkg_rwstat_recursive_sum() reads pos_blkg->online without the queue
lock that its doc comment requires, since blkcg_print_blkgs() stopped
holding it in 56cc24f59c. Concurrent blkg_create/destroy flips
->online, tripping KCSAN. The race is harmless (RCU-protected, stale
online only causes minor stat noise). Use data_race() to annotate
the intentional lockless read.
Also update the stale doc comment that still requires the queue lock.
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Signed-off-by: Tao Cui <cuitao@kylinos.cn>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://patch.msgid.link/20260803133400.137906-1-cui.tao@linux.dev
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Block device buffered reads and writes already pass through
filemap_read() and iomap_file_buffered_write() respectively, both of
which handle IOCB_DONTCACHE. Enable RWF_DONTCACHE for block device files
by setting FOP_DONTCACHE in def_blk_fops.
For CONFIG_BUFFER_HEAD=y, writeback goes through buffer_head's
__bh_submit() which sets BIO_COMPLETE_IN_TASK on dropbehind folios. For
CONFIG_BUFFER_HEAD=n, writeback goes through iomap which handles it via
BIO_COMPLETE_IN_TASK on the ioend bio.
This support is useful for databases that operate on raw block devices,
among other userspace applications.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-5-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Set BIO_COMPLETE_IN_TASK in __bh_submit() for write bios when the folio
has dropbehind set, so that buffer_head writeback completions get
deferred to task context where folio_end_dropbehind() can safely
invalidate folios.
Read completions are not deferred since dropbehind invalidation for
reads is handled synchronously by the reader.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-4-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Set BIO_COMPLETE_IN_TASK on iomap writeback bios when a dropbehind folio
is added. This ensures that bi_end_io runs in task context, where
folio_end_dropbehind() can safely invalidate folios.
With the bio layer now handling task-context deferral generically,
IOMAP_IOEND_DONTCACHE is no longer needed, as XFS no longer needs to
route DONTCACHE ioends through its completion workqueue. Remove the flag
and its NOMERGE entry.
Without the NOMERGE, regular I/Os that get merged with a dropbehind
folio will also have their completion deferred to task context.
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-3-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Some bio completion handlers need to run from preemptible task context,
but bio_endio() may be called from IRQ context (e.g., buffer_head
writeback). Callers need a way to ensure their callback eventually runs
from a sleepable context. Add infrastructure for that, in two forms:
1. BIO_COMPLETE_IN_TASK, a bio flag the submitter sets when it knows
in advance that its callback needs task context (e.g., dropbehind
writeback). bio_endio() sees the flag and offloads completion to a
worker automatically.
2. bio_complete_in_task(), a helper that completion callbacks can
invoke from within bi_end_io() when the deferral decision is
dynamic (e.g., fserror reporting).
Both share a per-CPU list drained by a work item on a WQ_PERCPU
workqueue. Producers push the bio onto the local CPU's list and schedule
the work item, which then dispatches each bio's bi_end_io() from task
context.
Both methods are gated on bio_in_atomic(), which returns true in any
context where a sleeping bi_end_io() is unsafe, including
non-preemptible task context.
Two CPU hotplug callbacks are used to drain remaining bios from the
departing CPU's batch, while maintaining the per-CPU behavior. The
CPUHP_AP_ONLINE_DYN callback disables the per-CPU work item while the
CPU is still online, preventing it from running on an unbound worker
later. CPUHP_BP_PREPARE_DYN then drains any bios added between disabling
the work item and CPU offline.
Link: https://lore.kernel.org/all/20260409160243.1008358-1-hch@lst.de/
Suggested-by: Matthew Wilcox <willy@infradead.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tal Zussman <tz2294@columbia.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260730-blk-dontcache-v7-2-3e8e6850068d@columbia.edu
Signed-off-by: Jens Axboe <axboe@kernel.dk>
