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Subject[PATCH AUTOSEL 5.0 59/98] sbitmap: order READ/WRITE freed instance and setting clear bit
Date
From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit e6d1fa584e0dd9bfebaf345e9feea588cf75ead2 ]

Inside sbitmap_queue_clear(), once the clear bit is set, it will be
visiable to allocation path immediately. Meantime READ/WRITE on old
associated instance(such as request in case of blk-mq) may be
out-of-order with the setting clear bit, so race with re-allocation
may be triggered.

Adds one memory barrier for ordering READ/WRITE of the freed associated
instance with setting clear bit for avoiding race with re-allocation.

The following kernel oops triggerd by block/006 on aarch64 may be fixed:

[ 142.330954] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000330
[ 142.338794] Mem abort info:
[ 142.341554] ESR = 0x96000005
[ 142.344632] Exception class = DABT (current EL), IL = 32 bits
[ 142.350500] SET = 0, FnV = 0
[ 142.353544] EA = 0, S1PTW = 0
[ 142.356678] Data abort info:
[ 142.359528] ISV = 0, ISS = 0x00000005
[ 142.363343] CM = 0, WnR = 0
[ 142.366305] user pgtable: 64k pages, 48-bit VAs, pgdp = 000000002a3c51c0
[ 142.372983] [0000000000000330] pgd=0000000000000000, pud=0000000000000000
[ 142.379777] Internal error: Oops: 96000005 [#1] SMP
[ 142.384613] Modules linked in: null_blk ib_isert iscsi_target_mod ib_srpt target_core_mod ib_srp scsi_transport_srp vfat fat rpcrdma sunrpc rdma_ucm ib_iser rdma_cm iw_cm libiscsi ib_umad scsi_transport_iscsi ib_ipoib ib_cm mlx5_ib ib_uverbs ib_core sbsa_gwdt crct10dif_ce ghash_ce ipmi_ssif sha2_ce ipmi_devintf sha256_arm64 sg sha1_ce ipmi_msghandler ip_tables xfs libcrc32c mlx5_core sdhci_acpi mlxfw ahci_platform at803x sdhci libahci_platform qcom_emac mmc_core hdma hdma_mgmt i2c_dev [last unloaded: null_blk]
[ 142.429753] CPU: 7 PID: 1983 Comm: fio Not tainted 5.0.0.cki #2
[ 142.449458] pstate: 00400005 (nzcv daif +PAN -UAO)
[ 142.454239] pc : __blk_mq_free_request+0x4c/0xa8
[ 142.458830] lr : blk_mq_free_request+0xec/0x118
[ 142.463344] sp : ffff00003360f6a0
[ 142.466646] x29: ffff00003360f6a0 x28: ffff000010e70000
[ 142.471941] x27: ffff801729a50048 x26: 0000000000010000
[ 142.477232] x25: ffff00003360f954 x24: ffff7bdfff021440
[ 142.482529] x23: 0000000000000000 x22: 00000000ffffffff
[ 142.487830] x21: ffff801729810000 x20: 0000000000000000
[ 142.493123] x19: ffff801729a50000 x18: 0000000000000000
[ 142.498413] x17: 0000000000000000 x16: 0000000000000001
[ 142.503709] x15: 00000000000000ff x14: ffff7fe000000000
[ 142.509003] x13: ffff8017dcde09a0 x12: 0000000000000000
[ 142.514308] x11: 0000000000000001 x10: 0000000000000008
[ 142.519597] x9 : ffff8017dcde09a0 x8 : 0000000000002000
[ 142.524889] x7 : ffff8017dcde0a00 x6 : 000000015388f9be
[ 142.530187] x5 : 0000000000000001 x4 : 0000000000000000
[ 142.535478] x3 : 0000000000000000 x2 : 0000000000000000
[ 142.540777] x1 : 0000000000000001 x0 : ffff00001041b194
[ 142.546071] Process fio (pid: 1983, stack limit = 0x000000006460a0ea)
[ 142.552500] Call trace:
[ 142.554926] __blk_mq_free_request+0x4c/0xa8
[ 142.559181] blk_mq_free_request+0xec/0x118
[ 142.563352] blk_mq_end_request+0xfc/0x120
[ 142.567444] end_cmd+0x3c/0xa8 [null_blk]
[ 142.571434] null_complete_rq+0x20/0x30 [null_blk]
[ 142.576194] blk_mq_complete_request+0x108/0x148
[ 142.580797] null_handle_cmd+0x1d4/0x718 [null_blk]
[ 142.585662] null_queue_rq+0x60/0xa8 [null_blk]
[ 142.590171] blk_mq_try_issue_directly+0x148/0x280
[ 142.594949] blk_mq_try_issue_list_directly+0x9c/0x108
[ 142.600064] blk_mq_sched_insert_requests+0xb0/0xd0
[ 142.604926] blk_mq_flush_plug_list+0x16c/0x2a0
[ 142.609441] blk_flush_plug_list+0xec/0x118
[ 142.613608] blk_finish_plug+0x3c/0x4c
[ 142.617348] blkdev_direct_IO+0x3b4/0x428
[ 142.621336] generic_file_read_iter+0x84/0x180
[ 142.625761] blkdev_read_iter+0x50/0x78
[ 142.629579] aio_read.isra.6+0xf8/0x190
[ 142.633409] __io_submit_one.isra.8+0x148/0x738
[ 142.637912] io_submit_one.isra.9+0x88/0xb8
[ 142.642078] __arm64_sys_io_submit+0xe0/0x238
[ 142.646428] el0_svc_handler+0xa0/0x128
[ 142.650238] el0_svc+0x8/0xc
[ 142.653104] Code: b9402a63 f9000a7f 3100047f 540000a0 (f9419a81)
[ 142.659202] ---[ end trace 467586bc175eb09d ]---

Fixes: ea86ea2cdced20057da ("sbitmap: ammortize cost of clearing bits")
Reported-and-bisected_and_tested-by: Yi Zhang <yi.zhang@redhat.com>
Cc: Yi Zhang <yi.zhang@redhat.com>
Cc: "jianchao.wang" <jianchao.w.wang@oracle.com>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>
---
lib/sbitmap.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 5b382c1244ed..155fe38756ec 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -591,6 +591,17 @@ EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);
void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
unsigned int cpu)
{
+ /*
+ * Once the clear bit is set, the bit may be allocated out.
+ *
+ * Orders READ/WRITE on the asssociated instance(such as request
+ * of blk_mq) by this bit for avoiding race with re-allocation,
+ * and its pair is the memory barrier implied in __sbitmap_get_word.
+ *
+ * One invariant is that the clear bit has to be zero when the bit
+ * is in use.
+ */
+ smp_mb__before_atomic();
sbitmap_deferred_clear_bit(&sbq->sb, nr);

/*
--
2.19.1
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