|From:||Manfred Spraul <manfred-AT-colorfullife.com>|
|To:||Davidlohr Bueso <davidlohr.bueso-AT-hp.com>, Michael Kerrisk <mtk.manpages-AT-gmail.com>, Martin Schwidefsky <schwidefsky-AT-de.ibm.com>|
|Subject:||[PATCH 0/4] ipc/shm.c: increase the limits for SHMMAX, SHMALL|
|Date:||Mon, 21 Apr 2014 16:26:33 +0200|
|Cc:||LKML <linux-kernel-AT-vger.kernel.org>, Andrew Morton <akpm-AT-linux-foundation.org>, KAMEZAWA Hiroyuki <kamezawa.hiroyu-AT-jp.fujitsu.com>, KOSAKI Motohiro <kosaki.motohiro-AT-jp.fujitsu.com>, gthelen-AT-google.com, aswin-AT-hp.com, linux-mm-AT-kvack.org, Manfred Spraul <manfred-AT-colorfullife.com>|
Hi all, the increase of SHMMAX/SHMALL is now a 4 patch series. I don't have ideas how to improve it further. The change itself is trivial, the only problem are interger overflows. The overflows are not new, but if we make huge values the default, then the code should be free from overflows. SHMMAX: - shmmem_file_setup places a hard limit on the segment size: MAX_LFS_FILESIZE. On 32-bit, the limit is > 1 TB, i.e. 4 GB-1 byte segments are possible. Rounded up to full pages the actual allocated size is 0. --> must be fixed, patch 3 - shmat: - find_vma_intersection does not handle overflows properly. --> must be fixed, patch 1 - the rest is fine, do_mmap_pgoff limits mappings to TASK_SIZE and checks for overflows (i.e.: map 2 GB, starting from addr=2.5GB fails). SHMALL: - after creating 8192 segments size (1L<<63)-1, shm_tot overflows and returns 0. --> must be fixed, patch 2. User space: - Obviuosly, there could be overflows in user space. There is nothing we can do, only use values smaller than ULONG_MAX. I ended with "ULONG_MAX - 1L<<24": - TASK_SIZE cannot be used because it is the size of the current task. Could be 4G if it's a 32-bit task on a 64-bit kernel. - The maximum size is not standardized across archs: I found TASK_MAX_SIZE, TASK_SIZE_MAX and TASK_SIZE_64. - Just in case some arch revives a 4G/4G split, nearly ULONG_MAX is a valid segment size. - Using "0" as a magic value for infinity is even worse, because right now 0 means 0, i.e. fail all allocations. Andrew: Could you add it into -akpm and move it towards linux-next? -- Manfred -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to email@example.com. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"firstname.lastname@example.org"> email@example.com </a>
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