From: Sagi Grimberg <sagi@grimberg.me>
To: Anton Eidelman <anton@lightbitslabs.com>,
linux-nvme@lists.infradead.org, hch@lst.de,
keith.busch@intel.com, hare@suse.de
Subject: Re: [PATCH] nvme-multipath: fix crash in nvme_mpath_clear_ctrl_paths
Date: Sun, 3 Nov 2019 06:31:15 -0800 [thread overview]
Message-ID: <c857ecec-7009-174f-ecb7-c43fd77212b9@grimberg.me> (raw)
In-Reply-To: <20191102002755.25165-1-anton@lightbitslabs.com>
> nvme_mpath_clear_ctrl_paths() iterates through
> the ctrl->namespaces list while holding ctrl->scan_lock.
> This does not seem to be the correct way of protecting
> from concurrent list modification.
>
> Specifically, nvme_scan_work() sorts ctrl->namespaces
> AFTER unlocking scan_lock.
>
> This may result in the following (rare) crash in ctrl disconnect
> during scan_work:
>
> BUG: kernel NULL pointer dereference, address: 0000000000000050
> Oops: 0000 [#1] SMP PTI
> CPU: 0 PID: 3995 Comm: nvme 5.3.5-050305-generic
> RIP: 0010:nvme_mpath_clear_current_path+0xe/0x90 [nvme_core]
> ...
> Call Trace:
> nvme_mpath_clear_ctrl_paths+0x3c/0x70 [nvme_core]
> nvme_remove_namespaces+0x35/0xe0 [nvme_core]
> nvme_do_delete_ctrl+0x47/0x90 [nvme_core]
> nvme_sysfs_delete+0x49/0x60 [nvme_core]
> dev_attr_store+0x17/0x30
> sysfs_kf_write+0x3e/0x50
> kernfs_fop_write+0x11e/0x1a0
> __vfs_write+0x1b/0x40
> vfs_write+0xb9/0x1a0
> ksys_write+0x67/0xe0
> __x64_sys_write+0x1a/0x20
> do_syscall_64+0x5a/0x130
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7f8d02bfb154
>
> Fix:
> After taking scan_lock in nvme_mpath_clear_ctrl_paths()
> down_read(&ctrl->namespaces_rwsem) as well to make list traversal safe.
> This will not cause deadlocks because taking scan_lock never happens
> while holding the namespaces_rwsem.
> Moreover, scan work downs namespaces_rwsem in the same order.
Thanks Anton, this looks good to me,
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
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next prev parent reply other threads:[~2019-11-03 14:31 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-02 0:27 [PATCH] nvme-multipath: fix crash in nvme_mpath_clear_ctrl_paths Anton Eidelman
2019-11-03 14:31 ` Sagi Grimberg [this message]
2019-11-04 23:55 ` Christoph Hellwig
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