mirror of https://github.com/torvalds/linux.git
070ad7e793
There are several races in floppy driver between bottom half (scheduled_work) and timers (fd_timeout, fd_timer). Due to slowness of the actual floppy devices, those races are never (at least to my knowledge) triggered on a bare floppy metal. However on virtualized (emulated) floppy drives, which are of course magnitudes faster than the real ones, these races trigger reliably. They usually exhibit themselves as NULL pointer dereferences during DMA setup, such as BUG: unable to handle kernel NULL pointer dereference at 0000000a [ ... snip ... ] EIP: 0060:[<c02053d5>] EFLAGS: 00010293 CPU: 0 EAX: ffffe000 EBX: 0000000a ECX: 00000000 EDX: 0000000a ESI: c05d2718 EDI: 00000000 EBP: 00000000 ESP: f540fe44 DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068 Process swapper (pid: 0, ti=f540e000 task=c082d5a0 task.ti=c0826000) Stack: ffffe000 00001ffc 00000000 00000000 00000000 c05d2718 c0708b40 f540fe80 c020470f c05d2718 c0708b40 00000000 f540fe80 0000000a f540fee4 00000000 c0708b40 f540fee4 00000000 00000000 c020526b 00000000 c05d2718 c0708b40 Call Trace: [<c020470f>] dump_trace+0xaf/0x110 [<c020526b>] show_trace_log_lvl+0x4b/0x60 [<c0205298>] show_trace+0x18/0x20 [<c05c5811>] dump_stack+0x6d/0x72 [<c0248527>] warn_slowpath_common+0x77/0xb0 [<c02485f3>] warn_slowpath_fmt+0x33/0x40 [<f7ec593c>] setup_DMA+0x14c/0x210 [floppy] [<f7ecaa95>] setup_rw_floppy+0x105/0x190 [floppy] [<c0256d08>] run_timer_softirq+0x168/0x2a0 [<c024e762>] __do_softirq+0xc2/0x1c0 [<c02042ed>] do_softirq+0x7d/0xb0 [<f54d8a00>] 0xf54d89ff but other instances can be easily seen as well. This can be observed at least under VMWare, VirtualBox and KVM. This patch converts all the timers and bottom halfs to be processed in a single workqueue. This aproach has been already discussed back in 2010 if I remember correctly, and Acked by Linus [1], but it then never made it to the tree. This all is based on original idea and code of Stephen Hemminger. I have ported original Stepen's code to the current state of the floppy driver, and performed quite some testing (on real hardware), which didn't reveal any issues (this includes not only writing and reading data, but also formatting (unfortunately I didn't find any Double-Density disks any more)). Ability to handle errors properly (supplying known bad floppies) has also been verified. [1] http://kerneltrap.org/mailarchive/linux-kernel/2010/6/11/4582092 Based-on-patch-by: Stephen Hemminger <shemminger@vyatta.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Jiri Kosina <jkosina@suse.cz> |
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