From: David Howells dhowells@redhat.com
[ Upstream commit 3f4aa981816368fe6b1d13c2bfbe76df9687e787 ]
When doing a partial writeback, afs_write_back_from_locked_page() may generate an FS.StoreData RPC request that writes out part of a file when a file has been constructed from pieces by doing seek, write, seek, write, ... as is done by ld.
The FS.StoreData RPC is given the current i_size as the file length, but the server basically ignores it unless the data length is 0 (in which case it's just a truncate operation). The revised file length returned in the result of the RPC may then not reflect what we suggested - and this leads to i_size getting moved backwards - which causes issues later.
Fix the client to take account of this by ignoring the returned file size unless the data version number jumped unexpectedly - in which case we're going to have to clear the pagecache and reload anyway.
This can be observed when doing a kernel build on an AFS mount. The following pair of commands produce the issue:
ld -m elf_x86_64 -z max-page-size=0x200000 --emit-relocs \ -T arch/x86/realmode/rm/realmode.lds \ arch/x86/realmode/rm/header.o \ arch/x86/realmode/rm/trampoline_64.o \ arch/x86/realmode/rm/stack.o \ arch/x86/realmode/rm/reboot.o \ -o arch/x86/realmode/rm/realmode.elf arch/x86/tools/relocs --realmode \ arch/x86/realmode/rm/realmode.elf \ >arch/x86/realmode/rm/realmode.relocs
This results in the latter giving:
Cannot read ELF section headers 0/18: Success
as the realmode.elf file got corrupted.
The sequence of events can also be driven with:
xfs_io -t -f \ -c "pwrite -S 0x58 0 0x58" \ -c "pwrite -S 0x59 10000 1000" \ -c "close" \ /afs/example.com/scratch/a
Fixes: 31143d5d515e ("AFS: implement basic file write support") Signed-off-by: David Howells dhowells@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/afs/inode.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/fs/afs/inode.c b/fs/afs/inode.c index 46d2d7cb461da..a74e8e209454b 100644 --- a/fs/afs/inode.c +++ b/fs/afs/inode.c @@ -171,6 +171,7 @@ static void afs_apply_status(struct afs_fs_cursor *fc, struct timespec64 t; umode_t mode; bool data_changed = false; + bool change_size = false;
BUG_ON(test_bit(AFS_VNODE_UNSET, &vnode->flags));
@@ -226,6 +227,7 @@ static void afs_apply_status(struct afs_fs_cursor *fc, } else { set_bit(AFS_VNODE_ZAP_DATA, &vnode->flags); } + change_size = true; } else if (vnode->status.type == AFS_FTYPE_DIR) { /* Expected directory change is handled elsewhere so * that we can locally edit the directory and save on a @@ -233,11 +235,19 @@ static void afs_apply_status(struct afs_fs_cursor *fc, */ if (test_bit(AFS_VNODE_DIR_VALID, &vnode->flags)) data_changed = false; + change_size = true; }
if (data_changed) { inode_set_iversion_raw(&vnode->vfs_inode, status->data_version); - afs_set_i_size(vnode, status->size); + + /* Only update the size if the data version jumped. If the + * file is being modified locally, then we might have our own + * idea of what the size should be that's not the same as + * what's on the server. + */ + if (change_size) + afs_set_i_size(vnode, status->size); } }