In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
netfs: Fix readahead synchronisation issues by loading all folios upfront<\/p>\n
There are some synchronisation issues that derive from the app thread
\nadding more folios to the rolling buffer whilst the collector thread is
\nlooking at them or trying to clear them, such as determining the setting of
\nfront_folio_order when the next folio hasn’t been added yet,<\/p>\n
The reason for the rolling buffer approach is that loading the buffer
\nupfront and then dropping all the refs just acquired is quite a slow
\noperation, and loading progressively allows some of the cost to be deferred
\nuntil after at least some of the I\/O is started.<\/p>\n
Instead, a better way is to load all the folios into the rolling buffer
\nupfront – and then drop the refs later, once the I\/O is in progress. (Even
\nbetter would be for the refs not to be there at all.)<\/p>\n
Fix this by changing the rolling buffer loader to load all the folios
\nselected by the VM for readahead upfront into the folio queue. The folio
\nqueue is allocated a batch worth at a time as we don’t know how many folios
\nare involved (the readahead_control struct, alas, has a page count, not a
\nfolio count).<\/p>\n
The folio refs acquired from readahead are then dropped in bulk once the
\nfirst subrequest is dispatched as it’s quite a slow operation. The
\ncollector waits for NETFS_RREQ_NEED_PUT_RA_REFS to be cleared so that it
\ndoesn’t unlock folios before the xarray has been scanned for them.<\/p>\n
This simplifies the buffer handling later and isn’t noticeably slower as
\nthe xarray doesn’t need to be modified and the folios are all already
\npre-locked.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
netfs: Fix readahead synchronisation issues by loading all folios upfront<\/p>\n
There are some synchronisation issues that derive from t<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-29272","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/29272","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=29272"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29272"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29272"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}