Date: Thu, 14 Feb 2019 17:21:09 +0000 From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 235747] vmem_bt_alloc() may leak reserved boundary tags Message-ID: <bug-235747-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235747 Bug ID: 235747 Summary: vmem_bt_alloc() may leak reserved boundary tags Product: Base System Version: CURRENT Hardware: powerpc OS: Any Status: New Severity: Affects Some People Priority: --- Component: kern Assignee: bugs@FreeBSD.org Reporter: markj@FreeBSD.org vmem_bt_alloc() is somewhat magical in that it must use the vmem allocator to allocate boundary tags for the vmem allocator. It uses a reserve of boundary tags and a global mutex to avoid infinite recursion. If the reserve somehow gets depleted, vmem_bt_alloc() effectively gets stuck and the system will grind to a halt; jhibbits has observed this happening on a powerpc64 platform. I think this can happen in the following scenario: vmem_bt_alloc() calls vmem_xalloc() on the per-domain kernel arena and puts some reserved boundary tags into the arena's pool. The attempt to allocate a KVA range subsequently fails because the per-domain arena has no free ranges and we cannot import from kernel_arena because it is too fragmented to satisfy a KVA_QUANTUM-sized allocation. So, vmem_xalloc() fails, leaving the reserved boundary tags up for grabs. Later, even if the per-domain kernel arena can satisfy an allocation for vmem_bt_alloc(), we may not have any boundary tags left to actually perform the allocation, and we're stuck. -- You are receiving this mail because: You are the assignee for the bug.home | help
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