Hi, On Sun 09-08-15 10:49:33, Sasha Levin wrote: > I saw the following warning while fuzzing with trinity: > > [385644.689209] WARNING: CPU: 1 PID: 23536 at mm/truncate.c:740 pagecache_isize_extended+0x124/0x180() > [385644.691780] Modules linked in: > [385644.692695] CPU: 1 PID: 23536 Comm: trinity-c242 Not tainted 4.2.0-rc5-next-20150806-sasha-00040-g1b47b00-dirty #2417 > [385644.695636] ffffffffb21300e0 ffff8800ba3cfc40 ffffffffb1e89dfc 0000000000000000 > [385644.708128] ffff8800ba3cfc80 ffffffffa8325106 ffffffffa869fdd4 ffff88006bbe1f10 > [385644.710046] 0000000000001007 ffff88006bbe1f60 ffff88006bbe1f10 ffff8803daa965a0 > [385644.722774] Call Trace: > [385644.723591] dump_stack (lib/dump_stack.c:52) > [385644.725180] warn_slowpath_common (kernel/panic.c:448) > [385644.728983] warn_slowpath_null (kernel/panic.c:482) > [385644.730679] pagecache_isize_extended (mm/truncate.c:740 (discriminator 1)) > [385644.732630] truncate_setsize (mm/truncate.c:710) > [385644.734469] v9fs_vfs_setattr_dotl (fs/9p/v9fs_vfs.h:81 fs/9p/vfs_inode_dotl.c:593) > [385644.753009] notify_change (fs/attr.c:270) > [385644.754303] do_truncate (fs/open.c:64) > [385644.759181] do_sys_ftruncate.constprop.5 (fs/open.c:193) > [385644.760669] SyS_ftruncate (fs/open.c:201) > [385644.761818] entry_SYSCALL_64_fastpath (arch/x86/entry/entry_64.S:186) > > But I'm not really sure how that happens... truncate_setsize() changes the inode > size before calling pagecache_isize_extended(): > > i_size_write(inode, newsize); > if (newsize > oldsize) > pagecache_isize_extended(inode, oldsize, newsize); > truncate_pagecache(inode, newsize); > > And notify_change() is verifying that i_mutex is held: > > WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex)); > > So it doesn't look like a race either. Well, looking at the code it can be a race which is specific to 9p filesystem. It seems to me that 9p can update i_size from v9fs_refresh_inode_dotl(). That can be called v9fs_lookup_revalidate() without holding i_mutex. Now I'm not sure d_revalidate() can really race with truncate on the same inode (whether there isn't something else protecting this). Al should know better... Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>