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If the method fails after calling rdma_explicit_destroy (eg if copy_to_user faults) then it will trigger a kernel oops: BUG: unable to handle kernel NULL pointer dereference at 0000000000000000 PGD 800000000548d067 P4D 800000000548d067 PUD 54a0067 PMD 0 SMP PTI CPU: 0 PID: 359 Comm: ibv_rc_pingpong Not tainted 4.18.0-rc1+ #28 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014 RIP: 0010: (null) Code: Bad RIP value. RSP: 0018:ffffc900001a3bf0 EFLAGS: 00010246 RAX: 0000000000000000 RBX: ffff88000603bd00 RCX: 0000000000000003 RDX: 0000000000000001 RSI: 0000000000000001 RDI: ffff88000603bd00 RBP: 0000000000000001 R08: ffffc900001a3cf8 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: ffffc900001a3cf0 R13: 0000000000000000 R14: ffffc900001a3cf0 R15: 0000000000000000 FS: 00007fb00dda8700(0000) GS:ffff880007c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: ffffffffffffffd6 CR3: 000000000548e004 CR4: 00000000003606b0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: ? rdma_lookup_put_uobject+0x22/0x50 [ib_uverbs] ? uverbs_finalize_object+0x3b/0x60 [ib_uverbs] ? uverbs_finalize_attrs+0x128/0x140 [ib_uverbs] ? ib_uverbs_cmd_verbs+0x698/0x7c0 [ib_uverbs] ? find_held_lock+0x2d/0x90 ? __might_fault+0x39/0x90 ? ib_uverbs_ioctl+0x111/0x1f0 [ib_uverbs] ? do_vfs_ioctl+0xa0/0x6d0 ? trace_hardirqs_on_caller+0xed/0x180 ? _raw_spin_unlock_irq+0x24/0x40 ? syscall_trace_enter+0x138/0x1d0 ? ksys_ioctl+0x35/0x60 ? __x64_sys_ioctl+0x11/0x20 ? do_syscall_64+0x5b/0x1c0 ? entry_SYSCALL_64_after_hwframe+0x49/0xbe This is because the type was replaced with the null_type during explicit destroy that cannot complete the destruction. One of the side effects of replacing the type is to make the object handle totally unreachable - so no other command could attempt to use it, even though it remains on the uboject list. We can get the same end result by just fully destroying the object inside rdma_explicit_destroy and leaving the caller the residual kref for the uobj with no attached HW object, and no presence in the ubojects list. Signed-off-by: Jason Gunthorpe <jgg@mellanox.com> Reviewed-by: Leon Romanovsky <leonro@mellanox.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.