On Thu, May 20, 2021 at 04:23:22PM +0800, Gao Xiang wrote: > Hi Darrick and Dave, > > On Wed, May 19, 2021 at 05:08:02PM -0700, Darrick J. Wong wrote: > > On Thu, May 20, 2021 at 08:20:06AM +1000, Dave Chinner wrote: > > > On Wed, May 19, 2021 at 02:02:05PM -0700, Darrick J. Wong wrote: > > > > Hm. Does anyone /else/ see failures with the new test xfs/168 (the fs > > > > shrink tests) on a 1k blocksize? It looks as though we shrink the AG so > > > > small that we trip the assert at the end of xfs_ag_resv_init that checks > > > > that the reservations for an AG don't exceed the free space in that AG, > > > > but tripping that doesn't return any error code, so xfs_ag_shrink_space > > > > commits the new fs size and presses on with even more shrinking until > > > > we've depleted AG 1 so thoroughly that the fs won't mount anymore. > > > > > > Yup, now that I've got the latest fstests I see that failure, too. > > > > > > [58972.431760] Call Trace: > > > [58972.432467] xfs_ag_resv_init+0x1d3/0x240 > > > [58972.433611] xfs_ag_shrink_space+0x1bf/0x360 > > > [58972.434801] xfs_growfs_data+0x413/0x640 > > > [58972.435894] xfs_file_ioctl+0x32f/0xd30 > > > [58972.439289] __x64_sys_ioctl+0x8e/0xc0 > > > [58972.440337] do_syscall_64+0x3a/0x70 > > > [58972.441347] entry_SYSCALL_64_after_hwframe+0x44/0xae > > > [58972.442741] RIP: 0033:0x7f7021755d87 > > > > > > > At a bare minimum we probably need to check the same thing the assert > > > > does and bail out of the shrink; or maybe we just need to create a > > > > function to adjust an AG's reservation to make that function less > > > > complicated. > > > > > > So if I'm reading xfs_ag_shrink_space() correctly, it doesn't > > > check what the new reservation will be and so it's purely looking at > > > whether the physical range can be freed or not? And when freeing > > > that physical range results in less free space in the AG than the > > > reservation requires, we pop an assert failure rather than failing > > > the reservation and undoing the shrink like the code is supposed to > > > do? > > > > Yes. I've wondered for a while now if that assert in xfs_ag_resv_init > > should get turned into an ENOSPC return so that callers can decide what > > they want to do with it. > > Thanks for the detailed analysis (sorry that I didn't check the 1k blocksize > case before), I'm now renting a department in a new city, no xfstests env > available for now. > > But if I read/understand correctly, the following code might resolve the issue? > > diff --git a/fs/xfs/libxfs/xfs_ag_resv.c b/fs/xfs/libxfs/xfs_ag_resv.c > index 6c5f8d10589c..1f918afd5e91 100644 > --- a/fs/xfs/libxfs/xfs_ag_resv.c > +++ b/fs/xfs/libxfs/xfs_ag_resv.c > @@ -312,10 +312,12 @@ xfs_ag_resv_init( > if (error) > return error; > > - ASSERT(xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved + > - xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved <= > - pag->pagf_freeblks + pag->pagf_flcount); > #endif > + if (xfs_perag_resv(pag, XFS_AG_RESV_METADATA)->ar_reserved + > + xfs_perag_resv(pag, XFS_AG_RESV_RMAPBT)->ar_reserved > > + pag->pagf_freeblks + pag->pagf_flcount) > + return -ENOSPC; > + > out: > return error; > } > > If that works, could you kindly send out it (or some better/sane solution), > many thanks in advance! That does seem to fix the symptoms, though I'm gonna take a closer look at the error handling elsewhere in that function. --D > > Thanks, > Gao Xiang > > > > > --D > > > > > IOWs, the problem is the ASSERT firing on debug kernels, not the > > > actual shrink code that does handle this reservation ENOSPC error > > > case properly? i.e. we've got something like an uncaught overflow > > > in xfs_ag_resv_init() that is tripping the assert? (e.g. used > > > > ask) > > > > > > So I'm not sure that the problem is the shrink code here - it should > > > undo a reservation failure just fine, but the reservation code is > > > failing before we get there on a debug kernel... > > > > > > Cheers, > > > > > > Dave. > > > -- > > > Dave Chinner > > > david@xxxxxxxxxxxxx
