[Bug libc/14958] New: Concurrent reader deadlock in pthread_rwlock_rdlock()

["daniel.stodden at gmail dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14958

             Bug #: 14958
           Summary: Concurrent reader deadlock in pthread_rwlock_rdlock()
           Product: glibc
           Version: 2.18
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: daniel.stodden@gmail.com
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


Created attachment 6780
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6780
Example program provoking concurrent reader deadlock.

We believe we found a deadlock scenario in NPTL's rwlock implementation, 
relating to additional scheduling dependencies which NPTL imposes on 
concurrent readers.

It happens when facing sufficient congestion between both 
read- and write-locking candidates queued.

The code attached was tested on eglibc 2.15, but we believe the same
issue remains present in any more recent version of glibc and eglibc
we've seen.

It contains additional comments and a description of an event series
which lead to readers never woken, despite the rwlock being held in
read-locked mode.

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