On Mon, 5 Nov 2007, Dave Hansen wrote: > > Actually, I think your s/while/if/ change is probably a decent fix. Any resemblance to a decent fix is purely coincidental. > Barring any other races, that loop should always have made progress on > mnt->__mnt_writers the way it is written. If we get to: > > > lock_and_coalesce_cpu_mnt_writer_counts(); > ----------------->HERE > > mnt_unlock_cpus(); > > and don't have a positive mnt->__mnt_writers, we know something is going > badly. We WARN_ON() there, which should at least give an earlier > warning that the system is not doing well. But it doesn't fix the > inevitable. Could you try the attached patch and see if it at least > warns you earlier? Thanks, Dave, yes, that gives me a nice warning: leak detected on mount(c25ebd80) writers count: -65537 WARNING: at fs/namespace.c:249 handle_write_count_underflow() [<c0103486>] show_trace_log_lvl+0x1b/0x2e [<c01034b6>] show_trace+0x16/0x1b [<c0103589>] dump_stack+0x19/0x1e [<c0171906>] handle_write_count_underflow+0x4c/0x60 [<c0171983>] mnt_drop_write+0x69/0x8e [<c0160211>] __fput+0xff/0x162 [<c016010d>] fput+0x2e/0x33 [<c01b8f63>] unionfs_file_release+0xc2/0x1c5 [<c01601a1>] __fput+0x8f/0x162 [<c016010d>] fput+0x2e/0x33 [<c015ec9d>] filp_close+0x50/0x5d [<c015ed1e>] sys_close+0x74/0xb4 [<c01026ce>] sysenter_past_esp+0x5f/0x85 and the test then goes quietly on its way instead of hanging. Though I imagine, with your patch or mine, that it's then making an unfortunate frequency of calls to lock_and_coalesce_longer_name_than_I_care_to_type thereafter. But it's hardly your responsibility to optimize for bugs elsewhere. The 2.6.23-mm1 tree has MNT_USER at 0x200, so I adjusted your flag to #define MNT_IMBALANCED_WRITE_COUNT 0x400 /* just for debugging */ > > I have a decent guess what the bug is, too. In the unionfs code: I'll let Erez take it from there... Hugh - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
