Messages in this thread | | | Subject | Re: [v2 PATCH] mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct | From | Yang Shi <> | Date | Tue, 27 Mar 2018 14:44:09 -0400 |
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On 3/27/18 3:32 AM, Cyrill Gorcunov wrote: > On Mon, Mar 26, 2018 at 05:59:49PM -0400, Yang Shi wrote: >>> Say we've two syscalls running prctl_set_mm_map in parallel, and imagine >>> one have @start_brk = 20 @brk = 10 and second caller has @start_brk = 30 >>> and @brk = 20. Since now the call is guarded by _read_ the both calls >>> unlocked and due to OO engine it may happen then when both finish >>> we have @start_brk = 30 and @brk = 10. In turn "write" semaphore >>> has been take to have consistent data on exit, either you have [20;10] >>> or [30;20] assigned not something mixed. >>> >>> That said I think using read-lock here would be a bug. >> Yes it sounds so. However, it was down_read before >> ddf1d398e517e660207e2c807f76a90df543a217 ("prctl: take mmap sem for writing >> to protect against others"). And, that commit is for fixing the concurrent >> writing to arg_* and env_*. I just checked that commit, but omitted the brk >> part. The potential issue mentioned by you should exist before that commit, >> but might be just not discovered or very rare to hit. >> >> I will change it back to down_write. > down_read before was a bug ;) And it was not discovered earlier simply > because not that many users of this interface exist, namely only criu > as far as I know by now.
Thanks for confirming this. I assumed so :-)
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