- 15 Jan, 2018 3 commits
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Roy Shterman authored
We need to ensure that delete_work will be hosted on a different workqueue than all the works we flush or cancel from it. Otherwise we may hit a circular dependency warning [1]. Also, given that delete_work flushes reset_work, host reset_work on nvme_reset_wq and delete_work on nvme_delete_wq. In addition, fix the flushing in the individual drivers to flush nvme_delete_wq when draining queued deletes. [1]: [ 178.491942] ============================================= [ 178.492718] [ INFO: possible recursive locking detected ] [ 178.493495] 4.9.0-rc4-c844263313a8-lb #3 Tainted: G OE [ 178.494382] --------------------------------------------- [ 178.495160] kworker/5:1/135 is trying to acquire lock: [ 178.495894] ( [ 178.496120] "nvme-wq" [ 178.496471] ){++++.+} [ 178.496599] , at: [ 178.496921] [<ffffffffa70ac206>] flush_work+0x1a6/0x2d0 [ 178.497670] but task is already holding lock: [ 178.498499] ( [ 178.498724] "nvme-wq" [ 178.499074] ){++++.+} [ 178.499202] , at: [ 178.499520] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0 [ 178.500343] other info that might help us debug this: [ 178.501269] Possible unsafe locking scenario: [ 178.502113] CPU0 [ 178.502472] ---- [ 178.502829] lock( [ 178.503115] "nvme-wq" [ 178.503467] ); [ 178.503716] lock( [ 178.504001] "nvme-wq" [ 178.504353] ); [ 178.504601] *** DEADLOCK *** [ 178.505441] May be due to missing lock nesting notation [ 178.506453] 2 locks held by kworker/5:1/135: [ 178.507068] #0: [ 178.507330] ( [ 178.507598] "nvme-wq" [ 178.507726] ){++++.+} [ 178.508079] , at: [ 178.508173] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0 [ 178.509004] #1: [ 178.509265] ( [ 178.509532] (&ctrl->delete_work) [ 178.509795] ){+.+.+.} [ 178.510145] , at: [ 178.510239] [<ffffffffa70ad6c2>] process_one_work+0x162/0x6a0 [ 178.511070] stack backtrace: : [ 178.511693] CPU: 5 PID: 135 Comm: kworker/5:1 Tainted: G OE 4.9.0-rc4-c844263313a8-lb #3 [ 178.512974] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.1-1ubuntu1 04/01/2014 [ 178.514247] Workqueue: nvme-wq nvme_del_ctrl_work [nvme_tcp] [ 178.515071] ffffc2668175bae0 ffffffffa7450823 ffffffffa88abd80 ffffffffa88abd80 [ 178.516195] ffffc2668175bb98 ffffffffa70eb012 ffffffffa8d8d90d ffff9c472e9ea700 [ 178.517318] ffff9c472e9ea700 ffff9c4700000000 ffff9c4700007200 ab83be61bec0d50e [ 178.518443] Call Trace: [ 178.518807] [<ffffffffa7450823>] dump_stack+0x85/0xc2 [ 178.519542] [<ffffffffa70eb012>] __lock_acquire+0x17d2/0x18f0 [ 178.520377] [<ffffffffa75839a7>] ? serial8250_console_putchar+0x27/0x30 [ 178.521330] [<ffffffffa7583980>] ? wait_for_xmitr+0xa0/0xa0 [ 178.522174] [<ffffffffa70ac1eb>] ? flush_work+0x18b/0x2d0 [ 178.522975] [<ffffffffa70eb7cb>] lock_acquire+0x11b/0x220 [ 178.523753] [<ffffffffa70ac206>] ? flush_work+0x1a6/0x2d0 [ 178.524535] [<ffffffffa70ac229>] flush_work+0x1c9/0x2d0 [ 178.525291] [<ffffffffa70ac206>] ? flush_work+0x1a6/0x2d0 [ 178.526077] [<ffffffffa70a9cf0>] ? flush_workqueue_prep_pwqs+0x220/0x220 [ 178.527040] [<ffffffffa70ae7cf>] __cancel_work_timer+0x10f/0x1d0 [ 178.527907] [<ffffffffa70fecb9>] ? vprintk_default+0x29/0x40 [ 178.528726] [<ffffffffa71cb507>] ? printk+0x48/0x50 [ 178.529434] [<ffffffffa70ae8c3>] cancel_delayed_work_sync+0x13/0x20 [ 178.530381] [<ffffffffc042100b>] nvme_stop_ctrl+0x5b/0x70 [nvme_core] [ 178.531314] [<ffffffffc0403dcc>] nvme_del_ctrl_work+0x2c/0x50 [nvme_tcp] [ 178.532271] [<ffffffffa70ad741>] process_one_work+0x1e1/0x6a0 [ 178.533101] [<ffffffffa70ad6c2>] ? process_one_work+0x162/0x6a0 [ 178.533954] [<ffffffffa70adc4e>] worker_thread+0x4e/0x490 [ 178.534735] [<ffffffffa70adc00>] ? process_one_work+0x6a0/0x6a0 [ 178.535588] [<ffffffffa70adc00>] ? process_one_work+0x6a0/0x6a0 [ 178.536441] [<ffffffffa70b48cf>] kthread+0xff/0x120 [ 178.537149] [<ffffffffa70b47d0>] ? kthread_park+0x60/0x60 [ 178.538094] [<ffffffffa70b47d0>] ? kthread_park+0x60/0x60 [ 178.538900] [<ffffffffa78e332a>] ret_from_fork+0x2a/0x40 Signed-off-by:Roy Shterman <roys@lightbitslabs.com> Signed-off-by:
Sagi Grimberg <sagi@grimberg.me> Signed-off-by:
Christoph Hellwig <hch@lst.de>
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Sagi Grimberg authored
It may cause race by setting 'nvmeq' in nvme_init_request() because .init_request is called inside switching io scheduler, which may happen when the NVMe device is being resetted and its nvme queues are being freed and created. We don't have any sync between the two pathes. This patch changes the nvmeq allocation to occur at probe time so there is no way we can dereference it at init_request. [ 93.268391] kernel BUG at drivers/nvme/host/pci.c:408! [ 93.274146] invalid opcode: 0000 [#1] SMP [ 93.278618] Modules linked in: nfsv3 nfs_acl rpcsec_gss_krb5 auth_rpcgss nfsv4 dns_resolver nfs lockd grace fscache sunrpc ipmi_ssif vfat fat intel_rapl sb_edac x86_pkg_temp_thermal intel_powerclamp coretemp kvm_intel kvm irqbypass crct10dif_pclmul crc32_pclmul ghash_clmulni_intel iTCO_wdt intel_cstate ipmi_si iTCO_vendor_support intel_uncore mxm_wmi mei_me ipmi_devintf intel_rapl_perf pcspkr sg ipmi_msghandler lpc_ich dcdbas mei shpchp acpi_power_meter wmi dm_multipath ip_tables xfs libcrc32c sd_mod mgag200 i2c_algo_bit drm_kms_helper syscopyarea sysfillrect sysimgblt fb_sys_fops ttm drm ahci libahci nvme libata crc32c_intel nvme_core tg3 megaraid_sas ptp i2c_core pps_core dm_mirror dm_region_hash dm_log dm_mod [ 93.349071] CPU: 5 PID: 1842 Comm: sh Not tainted 4.15.0-rc2.ming+ #4 [ 93.356256] Hardware name: Dell Inc. PowerEdge R730xd/072T6D, BIOS 2.5.5 08/16/2017 [ 93.364801] task: 00000000fb8abf2a task.stack: 0000000028bd82d1 [ 93.371408] RIP: 0010:nvme_init_request+0x36/0x40 [nvme] [ 93.377333] RSP: 0018:ffffc90002537ca8 EFLAGS: 00010246 [ 93.383161] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000008 [ 93.391122] RDX: 0000000000000000 RSI: ffff880276ae0000 RDI: ffff88047bae9008 [ 93.399084] RBP: ffff88047bae9008 R08: ffff88047bae9008 R09: 0000000009dabc00 [ 93.407045] R10: 0000000000000004 R11: 000000000000299c R12: ffff880186bc1f00 [ 93.415007] R13: ffff880276ae0000 R14: 0000000000000000 R15: 0000000000000071 [ 93.422969] FS: 00007f33cf288740(0000) GS:ffff88047ba80000(0000) knlGS:0000000000000000 [ 93.431996] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 93.438407] CR2: 00007f33cf28e000 CR3: 000000047e5bb006 CR4: 00000000001606e0 [ 93.446368] Call Trace: [ 93.449103] blk_mq_alloc_rqs+0x231/0x2a0 [ 93.453579] blk_mq_sched_alloc_tags.isra.8+0x42/0x80 [ 93.459214] blk_mq_init_sched+0x7e/0x140 [ 93.463687] elevator_switch+0x5a/0x1f0 [ 93.467966] ? elevator_get.isra.17+0x52/0xc0 [ 93.472826] elv_iosched_store+0xde/0x150 [ 93.477299] queue_attr_store+0x4e/0x90 [ 93.481580] kernfs_fop_write+0xfa/0x180 [ 93.485958] __vfs_write+0x33/0x170 [ 93.489851] ? __inode_security_revalidate+0x4c/0x60 [ 93.495390] ? selinux_file_permission+0xda/0x130 [ 93.500641] ? _cond_resched+0x15/0x30 [ 93.504815] vfs_write+0xad/0x1a0 [ 93.508512] SyS_write+0x52/0xc0 [ 93.512113] do_syscall_64+0x61/0x1a0 [ 93.516199] entry_SYSCALL64_slow_path+0x25/0x25 [ 93.521351] RIP: 0033:0x7f33ce96aab0 [ 93.525337] RSP: 002b:00007ffe57570238 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 [ 93.533785] RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 00007f33ce96aab0 [ 93.541746] RDX: 0000000000000006 RSI: 00007f33cf28e000 RDI: 0000000000000001 [ 93.549707] RBP: 00007f33cf28e000 R08: 000000000000000a R09: 00007f33cf288740 [ 93.557669] R10: 00007f33cf288740 R11: 0000000000000246 R12: 00007f33cec42400 [ 93.565630] R13: 0000000000000006 R14: 0000000000000001 R15: 0000000000000000 [ 93.573592] Code: 4c 8d 40 08 4c 39 c7 74 16 48 8b 00 48 8b 04 08 48 85 c0 74 16 48 89 86 78 01 00 00 31 c0 c3 8d 4a 01 48 63 c9 48 c1 e1 03 eb de <0f> 0b 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 85 f6 53 48 89 [ 93.594676] RIP: nvme_init_request+0x36/0x40 [nvme] RSP: ffffc90002537ca8 [ 93.602273] ---[ end trace 810dde3993e5f14e ]--- Reported-by:
Yi Zhang <yi.zhang@redhat.com> Signed-off-by:
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Sagi Grimberg authored
Signed-off-by:
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- 14 Jan, 2018 1 commit
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Jens Axboe authored
A previous commit moved the clearing of rq->rq_flags later, but we may have already set RQF_MQ_INFLIGHT when that happens. Ensure that we correctly initialize rq->rq_flags to the right value. This is based on an original fix by Ming, just rewritten to not require a conditional. Fixes: 7c3fb70f ("block: rearrange a few request fields for better cache layout") Reviewed-by:
Mike Snitzer <snitzer@redhat.com> Signed-off-by:
Jens Axboe <axboe@kernel.dk>
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- 12 Jan, 2018 3 commits
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Jens Axboe authored
Looking at debug output, we see: ./000000009ddfa913/requeue_list:000000009646711c {.op=READ, .state=idle, gen=0x1 18, abort_gen=0x0, .cmd_flags=, .rq_flags=SORTED|1|SOFTBARRIER|IO_STAT, complete =0, .tag=-1, .internal_tag=217} Note the '1' between SORTED and SOFTBARRIER - that's because no name as defined for RQF_STARTED. Fixed that. Signed-off-by: -
Christoph Hellwig authored
The previous patch assigns interrupt vectors to all possible CPUs, so now hctx can be mapped to possible CPUs, this patch applies this fact to simplify queue mapping & schedule so that we don't need to handle CPU hotplug for dealing with physical CPU plug & unplug. With this simplication, we can work well on physical CPU plug & unplug, which is a normal use case for VM at least. Make sure we allocate blk_mq_ctx structures for all possible CPUs, and set hctx->numa_node for possible CPUs which are mapped to this hctx. And only choose the online CPUs for schedule. Reported-by:
Christian Borntraeger <borntraeger@de.ibm.com> Tested-by:
Stefan Haberland <sth@linux.vnet.ibm.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
Ming Lei <ming.lei@redhat.com> Signed-off-by:
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Christoph Hellwig authored
Currently we assign managed interrupt vectors to all present CPUs. This works fine for systems were we only online/offline CPUs. But in case of systems that support physical CPU hotplug (or the virtualized version of it) this means the additional CPUs covered for in the ACPI tables or on the command line are not catered for. To fix this we'd either need to introduce new hotplug CPU states just for this case, or we can start assining vectors to possible but not present CPUs. Reported-by:
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- 11 Jan, 2018 2 commits
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Bart Van Assche authored
This patch does not change any functionality but makes the blk_mq_mark_tag_wait() code slightly easier to read. Signed-off-by:
Bart Van Assche <bart.vanassche@wdc.com> Cc: Christoph Hellwig <hch@lst.de> Cc: Omar Sandoval <osandov@fb.com> Cc: Hannes Reinecke <hare@suse.de> Cc: Johannes Thumshirn <jthumshirn@suse.de> Signed-off-by:
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Arnd Bergmann authored
Selecting FAULT_INJECTION causes a Kconfig warning when CONFIG_DEBUG_KERNEL is not set: warning: (BLK_DEV_NULL_BLK && DRM_I915_SELFTEST) selects FAULT_INJECTION which has unmet direct dependencies (DEBUG_KERNEL) The other drivers that use FAULT_INJECTION tend to have a separate Kconfig symbol for turning on that feature, so let's do the same thing here. This may add a bit more complexity than we like, but it avoids the warning and is more consistent with the rest of the kernel. Fixes: 93b57046 ("null_blk: add option for managing IO timeouts") Signed-off-by:
Arnd Bergmann <arnd@arndb.de> Signed-off-by:
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- 10 Jan, 2018 17 commits
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Bart Van Assche authored
This patch avoids that sparse reports the following: block/blk-mq.c:637:33: warning: context imbalance in 'hctx_unlock' - unexpected unlock block/blk-mq.c:642:9: warning: context imbalance in 'hctx_lock' - wrong count at exit Signed-off-by:
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Paolo Bonzini authored
After the first few months, the message has not led to many bug reports. It's been almost five years now, and in practice the main source of it seems to be MTIOCGET that someone is using to detect tape devices. While we could whitelist it just like CDROM_GET_CAPABILITY, this patch just removes the message altogether. The patch also removes the "safe but not very useful" ioctl whitelist, as suggested by Christoph. I doubt anything is using most of those ioctls _in general_, let alone on a partition. Reviewed-by:
Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:
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Jens Axboe authored
Move completion related items (like the call single data) near the end of the struct, instead of mixing them in with the initial queueing related fields. Move queuelist below the bio structures. Then we have all queueing related bits in the first cache line. This yields a 1.5-2% increase in IOPS for a null_blk test, both for sync and for high thread count access. Sync test goes form 975K to 992K, 32-thread case from 20.8M to 21.2M IOPS. Reviewed-by:
Omar Sandoval <osandov@fb.com> Signed-off-by:
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Jens Axboe authored
We only have one atomic flag left. Instead of using an entire unsigned long for that, steal the bottom bit of the deadline field that we already reserved. Remove ->atomic_flags, since it's now unused. Reviewed-by:
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Jens Axboe authored
We reduce the resolution of request expiry, but since we're already using jiffies for this where resolution depends on the kernel configuration and since the timeout resolution is coarse anyway, that should be fine. Reviewed-by:
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Jens Axboe authored
We don't need this to be an atomic flag, it can be a regular flag. We either end up on the same CPU for the polling, in which case the state is sane, or we did the sleep which would imply the needed barrier to ensure we see the right state. Reviewed-by:
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Jens Axboe authored
We are missing ZONE_WRITE_LOCKED and MQ_TIMEOUT_EXPIRED, add them so the debugfs bits can decode them. Signed-off-by: -
Keith Busch authored
Uses common code for determining if an error should be retried on alternate path. Acked-by:
Hannes Reinecke <hare@suse.com> Signed-off-by:
Keith Busch <keith.busch@intel.com> Reviewed-by:
Johannes Thumshirn <jthumshirn@suse.de> Reviewed-by:
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Keith Busch authored
Uses common code for determining if an error should be retried on alternate path. Acked-by:
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Keith Busch authored
This patch provides a common decoder for block status path related errors that may be retried so various entities wishing to consult this do not have to duplicate this decision. Acked-by:
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Keith Busch authored
This removes nvme multipath's specific status decoding to see if failover is needed, using the generic blk_status_t that was decoded earlier. This abstraction from the raw NVMe status means all status decoding exists in one place. Acked-by:
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Keith Busch authored
This adds more NVMe status code translations to blk_status_t values, and captures all the current status codes NVMe multipath uses. Acked-by:
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Bart Van Assche authored
It is nontrivial to derive from the blk-mq source code when blk_mq_tags.active_queues is decremented. Hence add a comment that explains this. Signed-off-by:
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Richard Narron authored
UFS partitions from newer versions of FreeBSD 10 and 11 use relative addressing for their subpartitions. But older versions of FreeBSD still use absolute addressing just like OpenBSD and NetBSD. Instead of simply testing for a FreeBSD partition, the code needs to also test if the starting offset of the C subpartition is zero. https://bugzilla.kernel.org/show_bug.cgi?id=197733Signed-off-by:
Richard Narron <comet.berkeley@gmail.com> Signed-off-by:
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Jens Axboe authored
Use the fault injection framework to provide a way for null_blk to configure timeouts. This only works for queue_mode 1 and 2, since the bio mode doesn't have code for tracking timeouts. Let's say you want to have a 10% chance of timing out every 100,000 requests, and for 5 total timeouts, you could do: modprobe null_blk timeout="100000,10,0,5" This is useful for adding blktests to test that IO timeouts are handled appropriately. Signed-off-by: -
Chiara Bruschi authored
Commit '7b9e9361' ("blk-mq-sched: unify request finished methods") changed the old name of current bfq_finish_request method, but left it unchanged elsewhere in the code (related comments, part of function name bfq_put_rq_priv_body). This commit fixes all occurrences of the old name of this method by changing them into the current name. Fixes: 7b9e9361 ("blk-mq-sched: unify request finished methods") Reviewed-by:
Paolo Valente <paolo.valente@linaro.org> Signed-off-by:
Federico Motta <federico@willer.it> Signed-off-by:
Chiara Bruschi <bruschi.chiara@outlook.it> Signed-off-by:
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Ming Lei authored
This reverts commit a2d37968. If max segment size isn't 512-aligned, this patch won't work well. Also once multipage bvec is enabled, adjacent bvecs won't be physically contiguous if page is added via bio_add_page(), so we don't need this kind of complicated logic. Reported-by:
Dmitry Osipenko <digetx@gmail.com> Signed-off-by:
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- 09 Jan, 2018 14 commits
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Jens Axboe authored
This is needed to ensure that we actually handle timeouts. Without it, the queue_mode=1 path will never call blk_add_timer(), and the queue_mode=2 path will continually just return EH_RESET_TIMER and we never actually complete the offending request. This was used to test the new timeout code, and the changes around killing off REQ_ATOM_COMPLETE. Signed-off-by: -
Jens Axboe authored
It's not available if we don't have group io scheduling set, and there's no need to call it. Fixes: 0d52af59 ("block, bfq: release oom-queue ref to root group on exit") Signed-off-by:
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Michael Lyle authored
Otherwise, architectures that do negated adds of atomics (e.g. s390) to do atomic_sub fail in closure_set_stopped. Signed-off-by:
Michael Lyle <mlyle@lyle.org> Cc: Kent Overstreet <kent.overstreet@gmail.com> Reported-by:
kbuild test robot <lkp@intel.com> Signed-off-by:
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Bart Van Assche authored
Commit 3a025e1d ("Add optional check for bad kernel-doc comments") causes W=1 the kernel-doc script to be run and thereby causes several new warnings to appear when building the kernel with W=1. Fix the block layer kernel-doc headers such that the block layer again builds cleanly with W=1. Signed-off-by:
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Bart Van Assche authored
Change "nedeing" into "needing" and "caes" into "cases". Fixes: commit f906a6a0 ("blk-mq: improve tag waiting setup for non-shared tags") Signed-off-by:
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Jens Axboe authored
In some stupider versions of gcc, it complains: block/blk-mq.c: In function ‘blk_mq_complete_request’: ./include/linux/srcu.h:175:2: warning: ‘srcu_idx’ may be used uninitialized in this function [-Wmaybe-uninitialized] __srcu_read_unlock(sp, idx); ^ block/blk-mq.c:620:6: note: ‘srcu_idx’ was declared here int srcu_idx; ^ which is completely bogus, since we only use srcu_idx when hctx->flags & BLK_MQ_F_BLOCKING is set, and that's the case where hctx_lock() has initialized it. Just set it to '0' in the normal path in hctx_lock() to silence this annoying warning. Fixes: 04ced159 ("blk-mq: move hctx lock/unlock into a helper") Fixes: 5197c05e ("blk-mq: protect completion path with RCU") Signed-off-by: -
Tejun Heo authored
The RCU protection has been expanded to cover both queueing and completion paths making ->queue_rq_srcu a misnomer. Rename it to ->srcu as suggested by Bart. Signed-off-by:
Tejun Heo <tj@kernel.org> Cc: Bart Van Assche <Bart.VanAssche@wdc.com> Signed-off-by:
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Tejun Heo authored
After the recent updates to use generation number and state based synchronization, we can easily replace REQ_ATOM_STARTED usages by adding an extra state to distinguish completed but not yet freed state. Add MQ_RQ_COMPLETE and replace REQ_ATOM_STARTED usages with blk_mq_rq_state() tests. REQ_ATOM_STARTED no longer has any users left and is removed. Signed-off-by:
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Tejun Heo authored
After the recent updates to use generation number and state based synchronization, blk-mq no longer depends on REQ_ATOM_COMPLETE except to avoid firing the same timeout multiple times. Remove all REQ_ATOM_COMPLETE usages and use a new rq_flags flag RQF_MQ_TIMEOUT_EXPIRED to avoid firing the same timeout multiple times. This removes atomic bitops from hot paths too. v2: Removed blk_clear_rq_complete() from blk_mq_rq_timed_out(). v3: Added RQF_MQ_TIMEOUT_EXPIRED flag. Signed-off-by:
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Tejun Heo authored
With issue/complete and timeout paths now using the generation number and state based synchronization, blk_abort_request() is the only one which depends on REQ_ATOM_COMPLETE for arbitrating completion. There's no reason for blk_abort_request() to be a completely separate path. This patch makes blk_abort_request() piggyback on the timeout path instead of trying to terminate the request directly. This removes the last dependency on REQ_ATOM_COMPLETE in blk-mq. Note that this makes blk_abort_request() asynchronous - it initiates abortion but the actual termination will happen after a short while, even when the caller owns the request. AFAICS, SCSI and ATA should be fine with that and I think mtip32xx and dasd should be safe but not completely sure. It'd be great if people who know the drivers take a look. v2: - Add comment explaining the lack of synchronization around ->deadline update as requested by Bart. Signed-off-by: -
Tejun Heo authored
blk_mq_check_inflight() and blk_mq_poll_hybrid_sleep() test REQ_ATOM_COMPLETE to determine the request state. Both uses are speculative and we can test REQ_ATOM_STARTED and blk_mq_rq_state() for equivalent results. Replace the tests. This will allow removing REQ_ATOM_COMPLETE usages from blk-mq. Signed-off-by:
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Tejun Heo authored
Currently, blk-mq timeout path synchronizes against the usual issue/completion path using a complex scheme involving atomic bitflags, REQ_ATOM_*, memory barriers and subtle memory coherence rules. Unfortunately, it contains quite a few holes. There's a complex dancing around REQ_ATOM_STARTED and REQ_ATOM_COMPLETE between issue/completion and timeout paths; however, they don't have a synchronization point across request recycle instances and it isn't clear what the barriers add. blk_mq_check_expired() can easily read STARTED from N-2'th iteration, deadline from N-1'th, blk_mark_rq_complete() against Nth instance. In fact, it's pretty easy to make blk_mq_check_expired() terminate a later instance of a request. If we induce 5 sec delay before time_after_eq() test in blk_mq_check_expired(), shorten the timeout to 2s, and issue back-to-back large IOs, blk-mq starts timing out requests spuriously pretty quickly. Nothing actually timed out. It just made the call on a recycle instance of a request and then terminated a later instance long after the original instance finished. The scenario isn't theoretical either. This patch replaces the broken synchronization mechanism with a RCU and generation number based one. 1. Each request has a u64 generation + state value, which can be updated only by the request owner. Whenever a request becomes in-flight, the generation number gets bumped up too. This provides the basis for the timeout path to distinguish different recycle instances of the request. Also, marking a request in-flight and setting its deadline are protected with a seqcount so that the timeout path can fetch both values coherently. 2. The timeout path fetches the generation, state and deadline. If the verdict is timeout, it records the generation into a dedicated request abortion field and does RCU wait. 3. The completion path is also protected by RCU (from the previous patch) and checks whether the current generation number and state match the abortion field. If so, it skips completion. 4. The timeout path, after RCU wait, scans requests again and terminates the ones whose generation and state still match the ones requested for abortion. By now, the timeout path knows that either the generation number and state changed if it lost the race or the completion will yield to it and can safely timeout the request. While it's more lines of code, it's conceptually simpler, doesn't depend on direct use of subtle memory ordering or coherence, and hopefully doesn't terminate the wrong instance. While this change makes REQ_ATOM_COMPLETE synchronization unnecessary between issue/complete and timeout paths, REQ_ATOM_COMPLETE isn't removed yet as it's still used in other places. Future patches will move all state tracking to the new mechanism and remove all bitops in the hot paths. Note that this patch adds a comment explaining a race condition in BLK_EH_RESET_TIMER path. The race has always been there and this patch doesn't change it. It's just documenting the existing race. v2: - Fixed BLK_EH_RESET_TIMER handling as pointed out by Jianchao. - s/request->gstate_seqc/request->gstate_seq/ as suggested by Peter. - READ_ONCE() added in blk_mq_rq_update_state() as suggested by Peter. v3: - Fixed possible extended seqcount / u64_stats_sync read looping spotted by Peter. - MQ_RQ_IDLE was incorrectly being set in complete_request instead of free_request. Fixed. v4: - Rebased on top of hctx_lock() refactoring patch. - Added comment explaining the use of hctx_lock() in completion path. v5: - Added comments requested by Bart. - Note the addition of BLK_EH_RESET_TIMER race condition in the commit message. Signed-off-by: -
Tejun Heo authored
Currently, blk-mq protects only the issue path with RCU. This patch puts the completion path under the same RCU protection. This will be used to synchronize issue/completion against timeout by later patches, which will also add the comments. Signed-off-by:
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Jens Axboe authored
Move the RCU vs SRCU logic into lock/unlock helpers, which makes the actual functional bits within the locked region much easier to read. tj: Reordered in front of timeout revamp patches and added the missing blk_mq_run_hw_queue() conversion. Signed-off-by:
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