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Differential D27522

fd: make serialization in fdescfree_fds conditional on hold count
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Authored by mjg on Dec 9 2020, 2:44 PM.
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markj
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rS368516: fd: make serialization in fdescfree_fds conditional on hold count
Summary

p_fd nullification in fdescfree serializes against new threads transitioning the count 1 -> 2, meaning that fdescfree_fds observing the count of 1 can safely assume there is nobody else using the table. Losing the race and observing > 1 is harmless.

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rS FreeBSD src repository - subversion
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mjg requested review of this revision.Dec 9 2020, 2:44 PM
mjg created this revision.
markj accepted this revision.Dec 10 2020, 2:57 PM
markj added inline comments.
sys/kern/kern_descrip.c
2470 ↗(On Diff #80477)

It would be worth adding a sentence explaining why we know that fd_holdcnt can't increase at this point.

This revision is now accepted and ready to land.Dec 10 2020, 2:57 PM
Closed by commit rS368516: fd: make serialization in fdescfree_fds conditional on hold count (authored by mjg). · Explain WhyDec 10 2020, 5:17 PM
This revision was automatically updated to reflect the committed changes.
mjg added a commit: rS368516: fd: make serialization in fdescfree_fds conditional on hold count.
Herald added a subscriber: imp. · View Herald TranscriptDec 10 2020, 5:17 PM

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kern/
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head/sys/kern/kern_descrip.c

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