Hello,
Commit ab6f762f0f53162d41 Linus' HEAD.
printk_deferred() does not make sure that it's safe to write to per-CPU data, which causes problems when printk_deferred() is invoked "too early", before per-CPU areas are initialized. There are multiple bug reports, e.g. https://bugzilla.kernel.org/show_bug.cgi?id=206847
-ss
On Tue, Apr 14, 2020 at 09:06:13PM +0900, Sergey Senozhatsky wrote:
Hello,
Commit ab6f762f0f53162d41 Linus' HEAD.
printk_deferred() does not make sure that it's safe to write to per-CPU data, which causes problems when printk_deferred() is invoked "too early", before per-CPU areas are initialized. There are multiple bug reports, e.g. https://bugzilla.kernel.org/show_bug.cgi?id=206847
-ss
So where do you want this commit backported to?
thanks, greg k-h
On (20/04/14 14:14), Greg KH wrote:
On Tue, Apr 14, 2020 at 09:06:13PM +0900, Sergey Senozhatsky wrote:
Hello,
Commit ab6f762f0f53162d41 Linus' HEAD.
printk_deferred() does not make sure that it's safe to write to per-CPU data, which causes problems when printk_deferred() is invoked "too early", before per-CPU areas are initialized. There are multiple bug reports, e.g. https://bugzilla.kernel.org/show_bug.cgi?id=206847
-ss
So where do you want this commit backported to?
Well, printk() is affected in all the kernels where printk_deferred() relies on per-CPU data. Which may translate to "pretty much all current stable kernels?" This patch, however, uses printk_safe() bits, so it won't apply on pre-printk_safe() kernels (not sure if we have such -stable kernels though).
-ss
On Tue, Apr 14, 2020 at 10:13:09PM +0900, Sergey Senozhatsky wrote:
On (20/04/14 14:14), Greg KH wrote:
On Tue, Apr 14, 2020 at 09:06:13PM +0900, Sergey Senozhatsky wrote:
Hello,
Commit ab6f762f0f53162d41 Linus' HEAD.
printk_deferred() does not make sure that it's safe to write to per-CPU data, which causes problems when printk_deferred() is invoked "too early", before per-CPU areas are initialized. There are multiple bug reports, e.g. https://bugzilla.kernel.org/show_bug.cgi?id=206847
-ss
So where do you want this commit backported to?
Well, printk() is affected in all the kernels where printk_deferred() relies on per-CPU data. Which may translate to "pretty much all current stable kernels?" This patch, however, uses printk_safe() bits, so it won't apply on pre-printk_safe() kernels (not sure if we have such -stable kernels though).
This is already in the 5.4.y tree, so I've added it to 4.19.y, but I could not apply it to anything older (4.14.y, 4.9.y, 4.4.y) as it did not apply there.
If you want it in those older kernels, and you think it is really needed, please feel free to send a backported version for them.
thanks,
greg k-h
linux-stable-mirror@lists.linaro.org
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Greg KH -
Sergey Senozhatsky