diff options
author | Roland Dreier <rolandd@cisco.com> | 2008-01-25 14:15:42 -0800 |
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committer | Roland Dreier <rolandd@cisco.com> | 2008-01-25 14:15:42 -0800 |
commit | 2fe7e6f7c9f55eac24c5b3cdf56af29ab9b0ca81 (patch) | |
tree | 0e3712ae9033d133e839a22ac28144215a7ece4a /Documentation/rocket.txt | |
parent | cf9542aa923982428fbf6a6f815c32ae2c3da8c7 (diff) |
IB/umad: Simplify and fix locking
In addition to being overly complex, the locking in user_mad.c is
broken: there were multiple reports of deadlocks and lockdep warnings.
In particular it seems that a single thread may end up trying to take
the same rwsem for reading more than once, which is explicitly
forbidden in the comments in <linux/rwsem.h>.
To solve this, we change the locking to use plain mutexes instead of
rwsems. There is one mutex per open file, which protects the contents
of the struct ib_umad_file, including the array of agents and list of
queued packets; and there is one mutex per struct ib_umad_port, which
protects the contents, including the list of open files. We never
hold the file mutex across calls to functions like ib_unregister_mad_agent(),
which can call back into other ib_umad code to queue a packet, and we
always hold the port mutex as long as we need to make sure that a
device is not hot-unplugged from under us.
This even makes things nicer for users of the -rt patch, since we
remove calls to downgrade_write() (which is not implemented in -rt).
Signed-off-by: Roland Dreier <rolandd@cisco.com>
Diffstat (limited to 'Documentation/rocket.txt')
0 files changed, 0 insertions, 0 deletions