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scst: document nolockdep patches

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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@7078 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Vladislav Bolkhovitin
2016-12-21 03:39:24 +00:00
parent 5e73767a1b
commit bdfc767077
1 changed files with 17 additions and 0 deletions
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scst/kernel/README_nolockdep Normal file
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In some cases SCST needs to take multiple locks recursivly, e.g. to lock
all tgt_devs in a session. For this case SCST takes those locks in their
current sort order, e.g. by LUN for tgt_devs, then releases in the
opposite order. Unfortunately, lockdep complains on such actions as
recursive locking, then disables itself. The disabling itself action is
the most unpleasant one leading to lockdep being useless after this
point.
Unfortunately, nested locking annotations can't help, because after
free, then alloc again, or after LUN change (in case of tgt_devs) order
of locks can change.
So, SCST has a set of nolockdep-x.y patches together with "*_nolockdep"
locks to implement a way to annotate some lock and unlock actions as "no
lockdep", so lockdep will not track them.
This is a debug aid useful only with lockdep enabled kernels.