Handle wired pages on pager error.
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Authored by kib on Oct 8 2016, 5:17 PM.

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alc
markj

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rS307501: If vm_fault_hold(9) finds that fs.m is wired, do not free it after a

Summary

If vm_fault_hold(9) finds wired page after the pager error, do not free it, leave the page to the wire owner. E.g. the page might be a part of the invalidated buffer.

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rS FreeBSD src repository - subversion

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kib updated this revision to Diff 21185.Oct 8 2016, 5:17 PM

kib retitled this revision from to Handle wired pages on pager error..

kib updated this object.

kib edited the test plan for this revision. (Show Details)

kib added reviewers: alc, markj.

kib set the repository for this revision to rS FreeBSD src repository - subversion.

Herald added a subscriber: imp. · View Herald TranscriptOct 8 2016, 5:17 PM

kib added a child revision: D8198: Buffer pager for FFS..Oct 8 2016, 5:29 PM

kib added a subscriber: pho.

alc added inline comments.Oct 9 2016, 5:03 PM

sys/vm/vm_fault.c
722 ↗	(On Diff #21185)	Normally, we would only access the page's wire count with the page lock held. Is there a reason why we can safely access the page's wire count here without holding the page lock?
746 ↗	(On Diff #21185)	Ditto.

You are right.

In my case, the race was impossible because this situation (VM_PAGER_BAD) was only observed for the FFS pager, and one wired reference was from the buffer, which explains why the race which you noted did not realized in the tests.

Check wired_count under the page lock.

markj accepted this revision.Oct 10 2016, 5:36 PM

markj edited edge metadata.

markj added inline comments.