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29fe839976
We add the new state to the nfsi->open_states list, making it
potentially visible to other threads, before we've finished initializing
it.
That wasn't a problem when all the readers were also taking the i_lock
(as we do here), but since we switched to RCU, there's now a possibility
that a reader could see the partially initialized state.
Symptoms observed were a crash when another thread called
nfs4_get_valid_delegation() on a NULL inode, resulting in an oops like:
BUG: unable to handle page fault for address: ffffffffffffffb0 ...
RIP: 0010:nfs4_get_valid_delegation+0x6/0x30 [nfsv4] ...
Call Trace:
nfs4_open_prepare+0x80/0x1c0 [nfsv4]
__rpc_execute+0x75/0x390 [sunrpc]
? finish_task_switch+0x75/0x260
rpc_async_schedule+0x29/0x40 [sunrpc]
process_one_work+0x1ad/0x370
worker_thread+0x30/0x390
? create_worker+0x1a0/0x1a0
kthread+0x10c/0x130
? kthread_park+0x80/0x80
ret_from_fork+0x22/0x30
Fixes: 9ae075fdd1 "NFSv4: Convert open state lookup to use RCU"
Reviewed-by: Seiichi Ikarashi <s.ikarashi@fujitsu.com>
Tested-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
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.
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.