On Wed, Jul 16, 2025 at 06:02:34 PM +0200, Christoph Hellwig wrote: > On Wed, Jul 16, 2025 at 08:38:12AM -0700, Darrick J. Wong wrote: >> I've seen this happen maybe once or twice, I think the problem is that >> the symlink xfs_bmapi_write fails to allocate enough blocks to store the >> symlink target, doesn't notice, and then the actual target write runs >> out of blocks before it runs out of pathlen and kaboom. >> >> Probably the right answer is to ENOSPC if we can't allocate blocks, but >> I guess we did reserve free space so perhaps we just keep bmapi'ing >> until we get all the space we need? >> >> The weird part is that XFS_SYMLINK_MAPS should be large enough to fit >> all the target we need, so ... I don't know if bmapi_write is returning >> fewer than 3 nmaps because it hit ENOSPC or what? >> >> (and because I can't reproduce it reliably, I have not investigated >> further :() I think you are right. Most likely we were able to successfully allocate less than XFS_SYMLINK_MAPS (i.e. 3) and the next allocation only found free extents whose length were larger than 1 FSB. The test fills 90% of the filesystem and then punches holes at every other block used by each of the "filler" files. So the filesystem could have some "free extents" whose size is larger than 1 FSB. These larger free extents allowed the block reservation to succeed. During the test run, we could have consumed all the 1 FSB sized free extents and hence a later allocation attempt can fail since we were trying to allocate only 1 FSB sized extent. > > I guess the recent cleanups are not too blame then, or just slightly > changed the timing for me to have a streak to frequently hit it. > > xfs/538 is the alloc minlen test that injects getting back the minlen > or failing allocations if minlen > 1. I guess that interacts badly > somehow with the rather uncommon multi-map allocations. The only > other one is xfs_da_grow_inode_int, and that only for directories > with a larger directory block size, and as a fallback when the contig > allocations fails. It might be worth crafting a test doing a lot > of symlinking while doing that error injetion to trigger it more > reliably. I have modifed xfs/538 to perform only write* and symlink operations. Unfortunately, the test hasn't failed yet despite running for 27 iterations. I will let it run during the weekend. -- Chandan
