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Being a module parameter, it's possible to do:
# modprobe cifs drop_dir_cache=1
Which will lead to a crash, because cifs_tcp_ses_list hasn't been
initialized yet:
[ 168.242624] BUG: kernel NULL pointer dereference, address: 0000000000000010
[ 168.242952] #PF: supervisor read access in kernel mode
[ 168.243175] #PF: error_code(0x0000) - not-present page
[ 168.243394] PGD 0 P4D 0
[ 168.243524] Oops: Oops: 0000 [#1] SMP NOPTI
[ 168.243703] CPU: 2 UID: 0 PID: 1105 Comm: modprobe Not tainted 7.0.0-lku #5 PREEMPT(lazy)
[ 168.244054] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.17.0-2-g4f253b9b-prebuilt.qemu.org 04/01/2014
[ 168.244557] RIP: 0010:cifs_param_set_drop_dir_cache+0x7c/0x100 [cifs]
...
[ 168.248785] Call Trace:
[ 168.248915] <TASK>
[ 168.249023] parse_args+0x285/0x3a0
[ 168.249204] ? __pfx_unknown_module_param_cb+0x10/0x10
[ 168.249448] load_module+0x192b/0x1bb0
[ 168.249637] ? __pfx_unknown_module_param_cb+0x10/0x10
[ 168.249882] ? kernel_read_file+0x27d/0x2b0
[ 168.250088] init_module_from_file+0xce/0xf0
[ 168.250291] idempotent_init_module+0xfb/0x2f0
[ 168.250496] __x64_sys_finit_module+0x5a/0xa0
[ 168.250694] do_syscall_64+0xe0/0x5a0
[ 168.250863] ? exc_page_fault+0x65/0x160
[ 168.251050] entry_SYSCALL_64_after_hwframe+0x77/0x7f
[ 168.251284] RIP: 0033:0x7fcaa12b774d
Instead of fixing this with some kind of "is module initialized"
approach, this patch instead moves that functionality to procfs,
setting a write op for the existing open_dirs entry, where
writing a 0 to it will drop the cached directory entries.
Also make it available only when CONFIG_CIFS_DEBUG=y.
A small change needed now is to not call flush_delayed_work()
on invalidate_all_cached_dirs() when called from procfs (can't sleep in
that context).
So add a @sync arg to invalidate_all_cached_dirs() to control when to
flush the delayed works.
Fixes:
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History
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