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  1. Jun 04, 2009
    • Salman Qazi's avatar
      drivers/char/mem.c: avoid OOM lockup during large reads from /dev/zero · 730c586a
      Salman Qazi authored
      
      While running 20 parallel instances of dd as follows:
      
        #!/bin/bash
        for i in `seq 1 20`; do
                 dd if=/dev/zero of=/export/hda3/dd_$i bs=1073741824 count=1 &
        done
        wait
      
      on a 16G machine, we noticed that rather than just killing the processes,
      the entire kernel went down.  Stracing dd reveals that it first does an
      mmap2, which makes 1GB worth of zero page mappings.  Then it performs a
      read on those pages from /dev/zero, and finally it performs a write.
      
      The machine died during the reads.  Looking at the code, it was noticed
      that /dev/zero's read operation had been changed by
      557ed1fa ("remove ZERO_PAGE") from giving
      zero page mappings to actually zeroing the page.
      
      The zeroing of the pages causes physical pages to be allocated to the
      process.  But, when the process exhausts all the memory that it can, the
      kernel cannot kill it, as it is still in the kernel mode allocating more
      memory.  Consequently, the kernel eventually crashes.
      
      To fix this, I propose that when a fatal signal is pending during
      /dev/zero read operation, we simply return and let the user process die.
      
      Signed-off-by: default avatarSalman Qazi <sqazi@google.com>
      Cc: Nick Piggin <nickpiggin@yahoo.com.au>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      [ Modified error return and comment trivially.  - Linus]
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      730c586a
    • Rusty Russell's avatar
      lguest: fix 'unhandled trap 13' with CONFIG_CC_STACKPROTECTOR · 2cb7878a
      Rusty Russell authored
      
      We don't set up the canary; let's disable stack protector on boot.c so
      we can get into lguest_init, then set it up.  As a side effect,
      switch_to_new_gdt() sets up %fs for us properly too.
      
      Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
      Acked-by: default avatarTejun Heo <tj@kernel.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2cb7878a
  2. Jun 03, 2009
  3. Jun 02, 2009
  4. Jun 01, 2009
  5. May 31, 2009
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