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author | Hugh Dickins <hughd@google.com> | 2013-02-22 16:35:16 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-02-23 17:50:20 -0800 |
commit | ef4d43a8075891137ebc064e473d2e904971e933 (patch) | |
tree | a32216419976dca72813a107bf2200d1683341c4 /net/core | |
parent | 9c620e2bc5aa4256c102ada34e6c76204ed5898b (diff) | |
download | linux-3.10-ef4d43a8075891137ebc064e473d2e904971e933.tar.gz linux-3.10-ef4d43a8075891137ebc064e473d2e904971e933.tar.bz2 linux-3.10-ef4d43a8075891137ebc064e473d2e904971e933.zip |
ksm: stop hotremove lockdep warning
Complaints are rare, but lockdep still does not understand the way
ksm_memory_callback(MEM_GOING_OFFLINE) takes ksm_thread_mutex, and holds
it until the ksm_memory_callback(MEM_OFFLINE): that appears to be a
problem because notifier callbacks are made under down_read of
blocking_notifier_head->rwsem (so first the mutex is taken while holding
the rwsem, then later the rwsem is taken while still holding the mutex);
but is not in fact a problem because mem_hotplug_mutex is held
throughout the dance.
There was an attempt to fix this with mutex_lock_nested(); but if that
happened to fool lockdep two years ago, apparently it does so no longer.
I had hoped to eradicate this issue in extending KSM page migration not
to need the ksm_thread_mutex. But then realized that although the page
migration itself is safe, we do still need to lock out ksmd and other
users of get_ksm_page() while offlining memory - at some point between
MEM_GOING_OFFLINE and MEM_OFFLINE, the struct pages themselves may
vanish, and get_ksm_page()'s accesses to them become a violation.
So, give up on holding ksm_thread_mutex itself from MEM_GOING_OFFLINE to
MEM_OFFLINE, and add a KSM_RUN_OFFLINE flag, and wait_while_offlining()
checks, to achieve the same lockout without being caught by lockdep.
This is less elegant for KSM, but it's more important to keep lockdep
useful to other users - and I apologize for how long it took to fix.
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'net/core')
0 files changed, 0 insertions, 0 deletions