blk-mq: recover from stale cached request in blk_mq_submit_bio#767
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When submitting a bio to blk-mq, if the task should sleep after peeking a cached request, but before it pops it, the plug is flushed and calls blk_mq_free_plug_rqs, freeing the cached_rqs. The code had already warned of this possibility, and specifically popped the request before other known blocking calls, but it didn't handle a blocking GFP_NOIO alloc. Allocating the split bio or the integrity payload are two such cases that can block under high memory pressure. The blk-mq submit_bio function continues with the peeked request that was just freed and re-initialized, so the driver receives that request with a NULL'ed mq_hctx, and inevitably panics. Relevant kernel messages if you should encounter this condition, where the "WARNING" is the harbinger of the panic about to happen: ------------[ cut here ]------------ WARNING: CPU: 4 PID: 80820 at block/blk-mq.c:3071 blk_mq_submit_bio+0x2cf/0x5b0 ... BUG: kernel NULL pointer dereference, address: 0000000000000100 #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 6b367b067 P4D 6b367b067 PUD 6bb5eb067 PMD 0 Oops: Oops: 0000 [#1] SMP CPU: 4 UID: 36666 PID: 80820 Comm: IOUringThread0 Kdump: loaded Tainted: G S W 6.16.1-0_fbk3_0_gd6c130b80483 #1 NONE Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN Hardware name: Quanta Twin Lakes MP/Twin Lakes Passive MP, BIOS F09_3A23 12/08/2020 RIP: 0010:nvme_queue_rqs+0x93/0x180 Code: 44 24 48 00 00 00 00 4d 85 f6 74 19 49 8b 44 24 10 4c 3b b0 00 01 00 00 74 0b 4c 89 f7 4c 89 fe e8 c2 62 cd ff 49 8b 44 24 10 <4c> 8b b0 00 01 00 00 49 f7 46 78 01 00 00 00 74 1a 49 8b 3e 8b 8f RSP: 0018:ffffc9004a8f34a8 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff888c12b92920 RCX: 0000000000000020 RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff888c12b92920 RBP: 0000000000000000 R08: 000000000000000b R09: ffffffffffffffff R10: 0000000000092800 R11: 000000000002e000 R12: ffff88828e325c00 R13: 0000000000000000 R14: 0000000000000000 R15: ffffc9004a8f34a8 FS: 00007f7cf30e6640(0000) GS:ffff8890fa908000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000100 CR3: 00000006bb387006 CR4: 00000000007726f0 PKRU: 55555554 Call Trace: <TASK> blk_mq_dispatch_queue_requests+0x46/0x120 blk_mq_flush_plug_list+0x38/0x130 blk_add_rq_to_plug+0xa2/0x160 blk_mq_submit_bio+0x3ab/0x5b0 __submit_bio+0x3a/0x260 submit_bio_noacct_nocheck+0xc6/0x2b0 btrfs_submit_bbio+0x14d/0x520 ? btrfs_get_extent+0x43f/0x640 submit_extent_folio+0x31f/0x340 btrfs_do_readpage+0x2d7/0xac0 btrfs_readahead+0x142/0x200 ? clear_state_bit+0x520/0x520 read_pages+0x57/0x200 ? folio_alloc_noprof+0x10c/0x310 page_cache_ra_unbounded+0x28c/0x480 ? asm_sysvec_call_function+0x16/0x20 ? blk_cgroup_congested+0xa/0x50 ? page_cache_sync_ra+0x41/0x2d0 filemap_get_pages+0x347/0xd50 filemap_read+0xd3/0x500 ? 0xffffffff81000000 __io_read+0x111/0x440 io_read+0x23/0x90 __io_issue_sqe+0x40/0x120 io_issue_sqe+0x3f/0x3a0 io_submit_sqes+0x2bd/0x790 __se_sys_io_uring_enter+0x100/0xc10 ? eventfd_read+0x100/0x1f0 ? futex_wake+0x1b9/0x260 ? syscall_trace_enter+0x34/0x1d0 do_syscall_64+0x6a/0x250 entry_SYSCALL_64_after_hwframe+0x4b/0x53 RIP: 0033:0x95d621e Code: 8b 12 f6 c2 01 75 2a 84 c9 74 22 44 0f b6 d1 41 09 c2 8b bf cc 00 00 00 41 b9 08 00 00 00 b8 aa 01 00 00 31 d2 45 31 c0 0f 05 <48> 89 c6 89 f0 5d c3 83 c8 02 eb d5 cc cc cc cc cc cc 55 48 89 e5 RSP: 002b:00007f7cf30dc630 EFLAGS: 00000246 ORIG_RAX: 00000000000001aa RAX: ffffffffffffffda RBX: 00007f7d18907000 RCX: 00000000095d621e RDX: 0000000000000000 RSI: 0000000000000006 RDI: 00000000000004cf RBP: 00007f7cf30dc630 R08: 0000000000000000 R09: 0000000000000008 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 R13: 0000000000000001 R14: 00007f7d18907320 R15: 0000000000000009 </TASK> Fixes: b0077e2 ("blk-mq: make sure active queue usage is held for bio_integrity_prep()") Fixes: 7b4f36c ("block: ensure we hold a queue reference when using queue limits") Signed-off-by: Keith Busch <kbusch@kernel.org>
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Pull request for series with
subject: blk-mq: recover from stale cached request in blk_mq_submit_bio
version: 1
url: https://patchwork.kernel.org/project/linux-block/list/?series=1085314