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afs: Fix endless loop in directory parsing 

If a directory has a block with only ".__afsXXXX" files in it (from
uncompleted silly-rename), these .__afsXXXX files are skipped but without
advancing the file position in the dir_context.  This leads to
afs_dir_iterate() repeating the block again and again.

Fix this by making the code that skips the .__afsXXXX file also manually
advance the file position.

The symptoms are a soft lookup:

        watchdog: BUG: soft lockup - CPU#3 stuck for 52s! [check:5737]
        ...
        RIP: 0010:afs_dir_iterate_block+0x39/0x1fd
        ...
         ? watchdog_timer_fn+0x1a6/0x213
        ...
         ? asm_sysvec_apic_timer_interrupt+0x16/0x20
         ? afs_dir_iterate_block+0x39/0x1fd
         afs_dir_iterate+0x10a/0x148
         afs_readdir+0x30/0x4a
         iterate_dir+0x93/0xd3
         __do_sys_getdents64+0x6b/0xd4

This is almost certainly the actual fix for:

        https://bugzilla.kernel.org/show_bug.cgi?id=218496

Fixes: 57e9d49c54 ("afs: Hide silly-rename files from userspace")
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/786185.1708694102@warthog.procyon.org.uk
Reviewed-by: Marc Dionne <marc.dionne@auristor.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Markus Suvanto <markus.suvanto@gmail.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
David Howells 2024-02-23 13:15:02 +00:00 committed by Christian Brauner
parent d206a76d7d
commit 5f7a076466
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1 changed files with 3 additions and 1 deletions
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4
fs/afs/dir.c
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@ -479,8 +479,10 @@ static int afs_dir_iterate_block(struct afs_vnode *dvnode,
dire->u.name[0] == '.' &&
ctx->actor != afs_lookup_filldir &&
ctx->actor != afs_lookup_one_filldir &&
memcmp(dire->u.name, ".__afs", 6) == 0)
memcmp(dire->u.name, ".__afs", 6) == 0) {
ctx->pos = blkoff + next * sizeof(union afs_xdr_dirent);
continue;
}
/* found the next entry */
if (!dir_emit(ctx, dire->u.name, nlen,