Re: [PATCH 1/5]: ufs: missed brelse and wrong baseblk

From: Al Viro
Date: Sun Jun 18 2006 - 12:19:39 EST


Comment more on the entire series than on this patch: scenario that causes
trouble
* foo is a sparse file on ufs with 8Kb block/1Kb fragment
* process opens it writable and mmaps it shared
* it proceeds to dirty the pages
* fork
* parent and child do msync() on pages next to each other

I.e. we try to write adjacent pages that sit in the same block. At the
same time. Each will trigger an allocation and we'd better be very
careful, or we'll end up allocating the same block twice.
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