Date: Fri, 2 Dec 2016 16:11:32 +0800 From: Sepherosa Ziehau <sepherosa@gmail.com> To: Ryan Stone <rstone@freebsd.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r309372 - head/sys/sys Message-ID: <CAMOc5cz7uvuvUVMeoAyb%2BZ17j0jyEHFEGii=6KiVa6fx_fSfAw@mail.gmail.com> In-Reply-To: <201612012108.uB1L8g19026075@repo.freebsd.org> References: <201612012108.uB1L8g19026075@repo.freebsd.org>
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peek_clear_sc is added to address the issue you mentioned. IMHO, this commit weakens the proper assertion. On Fri, Dec 2, 2016 at 5:08 AM, Ryan Stone <rstone@freebsd.org> wrote: > Author: rstone > Date: Thu Dec 1 21:08:42 2016 > New Revision: 309372 > URL: https://svnweb.freebsd.org/changeset/base/309372 > > Log: > Fix a false positive in a buf_ring assert > > buf_ring contains an assert that checks whether an item being > enqueued already exists on the ring. There is a subtle bug in > this assert. An item can be returned by a peek() function and > freed, and then the consumer thread can be preempted before > calling advance(). If this happens the item appears to still be > on the queue, but another thread may allocate the item from the > free pool and wind up trying to enqueue it again, causing the > assert to trigger incorrectly. > > Fix this by skipping the head of the consumer's portion of the > ring, as this index is what will be returned by peek(). > > Sponsored by: Dell EMC Isilon > MFC After: 1 week > Differential Revision: https://reviews.freebsd.org/D8685 > Reviewed by: hselasky > > Modified: > head/sys/sys/buf_ring.h > > Modified: head/sys/sys/buf_ring.h > ============================================================================== > --- head/sys/sys/buf_ring.h Thu Dec 1 20:36:48 2016 (r309371) > +++ head/sys/sys/buf_ring.h Thu Dec 1 21:08:42 2016 (r309372) > @@ -67,11 +67,13 @@ buf_ring_enqueue(struct buf_ring *br, vo > uint32_t prod_head, prod_next, cons_tail; > #ifdef DEBUG_BUFRING > int i; > - for (i = br->br_cons_head; i != br->br_prod_head; > - i = ((i + 1) & br->br_cons_mask)) > - if(br->br_ring[i] == buf) > - panic("buf=%p already enqueue at %d prod=%d cons=%d", > - buf, i, br->br_prod_tail, br->br_cons_tail); > + if (br->br_cons_head != br->br_prod_head) { > + for (i = (br->br_cons_head + 1) & br->br_cons_mask; i != br->br_prod_head; > + i = ((i + 1) & br->br_cons_mask)) > + if(br->br_ring[i] == buf) > + panic("buf=%p already enqueue at %d prod=%d cons=%d", > + buf, i, br->br_prod_tail, br->br_cons_tail); > + } > #endif > critical_enter(); > do { > _______________________________________________ > svn-src-all@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/svn-src-all > To unsubscribe, send any mail to "svn-src-all-unsubscribe@freebsd.org" -- Tomorrow Will Never Die
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