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From: Linus Torvalds <torvalds@linux-foundation.org> To: Ingo Molnar <mingo@elte.hu> Cc: Roland McGrath <roland@redhat.com>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86_64 ia32 syscall restart fix Date: Fri, 29 Feb 2008 08:26:14 -0800 (PST) [thread overview] Message-ID: <alpine.LFD.1.00.0802290814320.17889@woody.linux-foundation.org> (raw) In-Reply-To: <20080229155207.GC27248@elte.hu> On Fri, 29 Feb 2008, Ingo Molnar wrote: > > * Roland McGrath <roland@redhat.com> wrote: > > > The code to restart syscalls after signals depends on checking for a > > negative orig_ax, and for particular negative -ERESTART* values in ax. > > These fields are 64 bits and for a 32-bit task they get zero-extended. > > The syscall restart behavior is lost, a regression from a native > > 32-bit kernel and from 64-bit tasks' behavior. This patch fixes the > > problem by doing sign-extension where it matters. For orig_ax, the > > only time the value should be -1 but winds up as 0x0ffffffff is via a > > 32-bit ptrace call. So the patch changes ptrace to sign-extend the > > 32-bit orig_eax value when it's stored; it doesn't change the checks > > on orig_ax, though it uses the new current_syscall() inline to better > > document the subtle importance of the used of signedness there. The > > ax value is stored a lot of ways and it seems hard to get them all > > sign-extended at their origins. So for that, we use the > > current_syscall_ret() to sign-extend it only for 32-bit tasks at the > > time of the -ERESTART* comparisons. > > thanks, applied. Btw, can we please try to keep commit log messages readable? The above "blob of text" could/should have more structure than being just one big block, and could have been structured as a few shorter paragraphs to make it easier to read: (1) problem description (2) patch description and (3) explanation of why patch was done it was done. I don't know about you guys, but I read a *lot* of emails (and commit messages), and I hate seeing big blobs of text without structure. Give it a few breaks to make it easier to read, like just making new paragraphs, ie something like: > The code to restart syscalls after signals depends on checking for a > negative orig_ax, and for particular negative -ERESTART* values in ax. > These fields are 64 bits and for a 32-bit task they get zero-extended. > The syscall restart behavior is lost, a regression from a native 32-bit > kernel and from 64-bit tasks' behavior. > > This patch fixes the problem by doing sign-extension where it matters. > For orig_ax, the only time the value should be -1 but winds up as > 0x0ffffffff is via a 32-bit ptrace call. So the patch changes ptrace to > sign-extend the 32-bit orig_eax value when it's stored; it doesn't > change the checks on orig_ax, though it uses the new current_syscall() > inline to better document the subtle importance of the used of > signedness there. > > The ax value is stored a lot of ways and it seems hard to get them all > sign-extended at their origins. So for that, we use the > current_syscall_ret() to sign-extend it only for 32-bit tasks at the > time of the -ERESTART* comparisons. and now you have a bit of a breather space and some visual cues for whare you are in the text. Yeah, maybe it's just me, but I like my whitespace. Ihaveareallyhardtime readingtextthatdoesn'thavethepropermarkersforwhereconceptsstartandbegin, andthatreallydoesincludetheverticalwhitespacetoo. Now, the only reason I mention this is that normally I would probably just have fixed this up myself without even a comment (because it's such a tiny detail that it's not not worth one), but when Ingo merges it I'll now get it through git and it will be fixed. Linus "yeah, I can be anal" Torvalds
next prev parent reply other threads:[~2008-02-29 16:27 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2008-02-29 3:57 [PATCH] x86_64 ia32 syscall restart fix Roland McGrath 2008-02-29 15:52 ` Ingo Molnar 2008-02-29 16:26 ` Linus Torvalds [this message] 2008-02-29 16:45 ` Ingo Molnar 2008-02-29 17:03 ` Linus Torvalds 2008-02-29 17:17 ` Ingo Molnar 2008-02-29 17:37 ` Ingo Molnar 2008-02-29 21:02 ` Andrew Morton 2008-02-29 21:20 ` Ingo Molnar 2008-03-01 5:48 ` [stable] " Greg KH 2008-02-29 22:42 ` Roland McGrath 2008-02-29 23:18 ` Linus Torvalds 2008-03-07 22:56 ` [PATCH] x86_64 ptrace orig_ax on ia32 task Roland McGrath 2008-03-07 23:18 ` Linus Torvalds 2008-03-08 1:37 ` Roland McGrath 2008-03-10 19:19 ` Chuck Ebbert 2008-03-10 19:48 ` Linus Torvalds 2008-03-10 20:01 ` Roland McGrath 2008-03-11 9:32 ` Ingo Molnar
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